Hm… I feel like for the kids who are clan heirs–rather than seconds–there would be some pressure to get married and have heirs. I mean, as we saw with Shikaku’s chapter of Sunshine Sidestories, there is still a very strong traditionalism–and even though that’s the generation before, I don’t think it would relax so much to allow no heirs whatsoever. In contrast, there is the possibility that heirs with seconds–such as Shikamaru with Shikako, Hana with Kiba, and Chiyako and Shino (who I am still unsure if he is the heir or not, but him being the older brother in a matrilineal clan is something that just resonates with me)–would be exempt from having children if their respective seconds have viable heirs instead (though given the seconds in question that’s kinda unlikely).
However, given that most of the kids are clan heirs and have been raised as such (with the understanding that they enjoy the benefits of the clan because they have duties to the clan) they probably also accept that having children eventually or preparing their heir is one of those duties. I mean, they don’t need to have children in their twenties, but I think if they’re nearing thirty and they’re not even married the elders of each respective clan would be worried…
I wonder about artificial insemination, though, because… like… does that exist in this future or not? Because if so, you’d think that canon!Sasuke would consider that to rebuild his clan? Or some of the more practical minded members of Konoha would want to revive such a powerful bloodline? And it’s not like Konoha as the forerunner of the health industry wouldn’t be able to figure it out?
Then again, given how Shippuden was basically “Uchiha melodrama almost destroys the world,” maybe a practical mind would want to prevent the revival of the Sharingan users.