This is really interesting.So what I'm suggesting instead is: on succession if it happens that your oldest son is not actually yours, he still inherits (because everyone around think they are), but you as a player end up playing the closest dynasty member who is its member in actuality and not just belief [among the landed ones for now, but since they said unlanded gameplay is not impossible in the future, imagine trying to retake the throne from an unlanded position].
This then makes it actually important to give land to your sons, since you can't be 100% sure which of them you'll end up playing as. And then when it happened you can try and regain the throne by pushing your claim, and you can plot against the main heir to discover and expose that they are a bastard, which should give them a large enough opinion malus for more vassals to back you in your faction.
Mainly because it makes you care about your dynasty as a whole (I know I was trying to land as many of my relatives as possible by giving them less important baronies/counties/duchies in order to get as much of the realm in the hands of my bloodline), rather than attempt to have one perfect heir to whom you give everything. But it also spices up the political intrigues, which is what keeps the game always interesting, no matter how powerful you are.
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