Integration of gender laws

Rhaenyra at the same time refused to accept Rosby's and Stokeworth's oldest daughters as their heirs over their younger brothers. She obviously didn't cared about equality but only about her claim.

If not Rhaenyra, then Deny-player should have this option for sure. Breaking the wheel then breaking all the wheels and all that.

I actually support this as well, mostly in light of Fire and Blood. There's been multiple great wars waged on behalf of female claimants to the Iron Throne. A Great Council did occur that created a precedent for males to precede females in the line of succession (which was a big deal in the history as written by the maesters). This is in itself is interesting since it's just as possible that the Great Council would have gone the other way, creating a precedent for true cognatic succession for the Iron Throne, which would have been equally important in determining the succession laws. In any case, considering the sheer number of extremely important females in the history of the Targaryen dynasty (as both warriors and important policy-setters), I don't see it being that far fetched for gender equality to become a thing somewhat more quickly.

That isn't exactly fair - Rhaenyra was claiming her right to rule, and Targs at the time were subject to Valyrian inheritance laws, which was equal, laws that the Rosby's and Stokeworth's wouldn't fall under, not being Valyrian. Targs had been following Valyrian ways for other things - incest marriage for one - yet the rest of Westeros didn't. So her seeing herself as an exception to that makes sense in context. Thus your fault of Rhaenyra isn't as logical or correct as you make it seem. What should be possible is for Targs at a minimum to be able to go to equal sex laws, while allowing the sub-regions to use patriarchal ones. Similar to how Dorne can be equal sex, while the rest of the realm is patriarchal.

Three bits of evidence against that mate.

1. Prince in High Valyrian has no gender assigned to it. It is known that this is not a "masculine" verb like Westeros wrongly assumed, it is in fact gender neutral, able to be used for both sexes. Hence why "Prince that was Promised" could be prince or princess. This is evidence that the Valyrians didn't give a damn about gender, only who was supposed to rule, who was heir. Further, since they weren't a kingdom, but instead a freehold of forty families, "prince" for them merely would have meant "heir" as in who was the next head of one of those families. Power is the only thing they cared about. Who was, and who wasn't, a dragonlord, and who among those dragonlords, was supposed to be in charge.

2. Targs can also designate their chosen successor, the first-born is just the assumed heir until that is done. This is also unique to them, as no other rulers in Westeros do this. Thus designation of an heir is a remnant of Valyrian tradition, rather than a Westerosi one. As such assuming Aegon was heir because he was male and not merely because he was a better choice over the other two is an assumption. It actually makes sense, they were all married together, and having one female over the other could only help foster a further rivalry - Visenya was already jealous that Rhaenys shared Aegon's bed more. Give her official power over Rhaenys by making Visenya the leader, and you'd have a recipe for mistreatment and then infighting - something that could not be afforded with so few dragons and dragonlords. Aegon's father was smarter than that. He realized it was simply better to have the male as heir in that particular case, so as to avoid causing infighting between the two female dragonlords. It's simple politics, not male preference.

Another possibility is that heir-ship was tied to which dragon you bonded with - the heir being the one with the most powerful dragon, because he or she could keep order by force if necessary. With Aegon bonded to Balerion, the largest of them all... Thus you have two very good reasons for why Aegon was leader, ways that make sense politically, despite him not being the first-born, without ignoring the facts about Valyrian language to suit a presupposed viewpoint. This is a matter of following the evidence, rather than assuming a position. Then there's always the simple fact that Aegon was simply a better ruler. Visenya was too harsh, and Rhaenys too... well not harsh enough. Aegon was a good leader, he knew when to be hard, when to bend - like when he bent to the Seven in order to get the others to surrender without having to fight more. He was diplomatic, and also a good warrior. Even without anything else, he was the superior choice by merit of his personality. Thus, there are many reasons for him to have been chosen as heir, other than simply his gender. As such, ignoring all the other evidence that the Valyrian way was equal among the genders, doesn't make any sense logically, unless you're pushing a narrative, or simply didn't know, or didn't consider the evidence fully.

3. The entire reason they had to have councils about this stuff, multiple times at that, was because male only heir-ship was not assumed, despite this being the case for all of Westeros (except Dorne) at the time. And frankly, Dorne wasn't even a part of the Iron Throne yet for some of those, so that isn't even a good excuse to run to if you're looking for one. So no, my argument isn't wrong by one little example when the very language of the Valyrians proves otherwise. You're looking only at the surface, rather than all the evidence. Surface views of anything are rarely correct, even moreso when looking into the culture of a dead people. Any historian would be able to tell you they were about gender equal inheritance from their language alone. Language can tell you a lot more about a culture than some biased Maesters writing history as they see fit.

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But honestly all this about Rhaenyra isn't even needed for this to be allowed. There is a simpler and even better point arguing for the ability of Targs to go to equal gender inheritance laws, and that is the mere fact that they had councils about allowing it! Them discussing the option, shows that Targs in-game should be allowed to change to equal inheritance law if they choose to, even without all this evidence, simply because they very nearly did multiple times. CKII is about alternate history not just replaying a set scenario. One of those would be "What if Rhaenyra did get crowned heir without a Dance?" "What if one of the multiple times the Council met about female heirship, it actually passed?"

Also the Targs should allow ruler designate succession, (though male-only without the gender law being changed as a Targ) as that had been done multiple times as well, and there were no special councils needed to do it.

1. There are plenty of languages that use gender-neutral forms of words, but it is not conclusive evidence that the sexes are considered equal. Many of the societies that used them were still patriarchal.

2. The notion that Aegon was the head of House Targaryen because of the political risks of sexual and romantic jealousies, while novel, is pretty far out there. The dragon idea is more interesting, but it is also pure theorizing, and not evidenced by the text. We do know that of the information we have, the head of House Targaryen was always the male when one was available.

3. Only the first great council had to do with male vs. female inheritance. First there was a fight between Jaehaerys and Alysanne when he skipped a grand daughter and considered his eldest son the heir. About a decade later the first council was called in response to a conflict between Viserys Targaryen and Laenor Velaryon. Laenor was the offspring of the king's grand daughter.

Both of these quarrels started with an assumption that the eldest male line member would be the heir. Alysanne was notorious for fighting for gender equality and detesting male supremacy, but she was unusual her devotion to it. But there was never really any major doubt among the majority of Targaryens or their supporters that males inherited before females.

The first great council did reaffirm the precedence of the male line before the female line, btw.

The second great council was a regency council. That Aegon had inherited the kingship was never in question.

The third great council was about deciding who their heir was when the inheritance was unclear due to a large number of deaths. Vaella was never even considered even though she was the only child of the former king's eldest son. Her claim was presented at the council but not taken seriously.

I think you may have misunderstood the great councils a bit.

3. As Paxter mentioned, GRRM is admittedly not good with languages. He says he never created any language, and the small pieces on the TV show had to be created independently for its use. We cannot make any real linguistic analysis of it, and it is certainly not grounded in or a guide to any historical political or family inheritance traditions.