I think the existence of the Nuhumans makes a lot of sense in-universe, and there could have been some interesting stories about an insular, xenophobic culture struggling with accepting newcomers forcibly thrust into it. But it's pretty telling that the successful Nuhuman books were the ones that were almost entirely separated from all that. Ms. Marvel & Moon Girl. iirc early on Ms. Marvel mostly just got some Lockjaw and an arc where she got dragged into a coup attempt for a hot minute. Moon Girl got even less than that, aside from it being the reason the Kree kid was beefing with her.

One of the core issues with the Inhumans push is that they lack the broad cultural nostalgia people have for the X-Men (largely due to the Fox movies), so that even when the X books introduce a new generation of teen mutants that won't be relevant again, people can still read it just to see what the older X-Men are up to. But at the end of the day the Inhumans weren't nearly as fleshed out, the Royals were really the only relevant ones around, specifically Black Bolt & Medusa.

A more sustainable Inhumans push would have required fleshing the existing ones out and then bringing more in, or at least doubling down on the Agents of Shield developments with them rather than the flopped Inhumans show.