The trouble in terms of political impact is that the "R's have 4 kids, D's have no kids" areas are very disproportionately megacities that vote 80%D/20%R today. That's a very low baseline to build from and in the short-medium run, it just makes their coalition less and less geographically efficient. In the near/medium term, the most likely positive impact for R's is 1. South Florida 2. keeping the Houston/Dallas/San Antonio metros close enough to save Texas 3. maybe keeping Virginia interesting.
I don't know that this is true; maps of white fertility tend to actually correspond pretty closely to 'GOP strength', although there's also just greater fertility in the Plains (especially) and Mountain West (less so).
https://twitter.com/Empty_America/status/1628790361152802818
One of the patterns is indeed that the conservative advantage grows the wealthier a community is (and you maybe see that with NJ marked a darker color on that map). But I don't know that wealthy communities with lots of kids are so disproportionately found in giant megacities, and I think that a big part of the effect will be rural areas in Plains states to some degree continuing to redden. (A county-by-county version of this map, which I'm struggling to find now, has lots of bleed from ND and SD into rural MN and IA; I think in those places there's still a while to go in terms of how far rural areas will trend Republican).
However, the flip side of this is Dems seeding several small Western/Plains states with WFH techies and certain states becoming "abortion tourism" destinations after all surrounding areas ban (looking at you, Kansas). That's why I don't think the impending permanent R senate/SCOTUS majority takes hold water anymore like they did pre-COVID. So I'm not expecting an all R appointed SCOTUS anytime soon. If anything, this is likely the R high water mark today.
KS is outright losing population, and it doesn't actually do very well in terms of attracting college graduates to live there. There's been an enormous Democratic trend among the ones they have, but in the super-long-run, if anything MO might be likelier to reverse.
Among current small deeply-R states, I think the only one with a very left-wing in-migration pattern is Alaska -- which I can easily see being very Democratic in a few decades, to be sure. But I think that the Supreme Court will move in the direction of whatever party has a Senate majority most of the time, and it's really hard to see that being the Democrats without some absolutely enormous realignment. I don't think the Court will even stop getting more conservative -- not even start getting more-progressive, just halt -- until there's a very lengthy period of consistent left-wing Senate control.
I agree with your implication that there isn't as much reason to suspect that higher fertility rates among
nonwhite US residents would benefit Rs on net, even if those voters are less D than their lower-fertility counterparts of various backgrounds.
Fascinating to see how many states experience net "brain drain" of college graduates, and that OR and TN do better than the median state despite being neutral on this metric.
