Technology

it takes upwards of 20 years to build a reactor. Even if that gets expedited through modern technologies, we’re still talking something like 15 years until they come online, and you’re still paying all the upfront costs throughout that time

From some reading, it seems a lot of that is bureaucracy (non-safety related), construction delays, and lawsuits. I wouldn't be surprised if we could get that down to 10 years average with a concerted effort, assuming we can build multiple in parallel.

Whereas solar can go from concept to grid in 2 years, and batteries aren’t much worse.

Sure, on a small-ish scale. A nuclear plant will put out way more electricity than a typical solar project will. So while the time to getting value from it will be a lot shorter w/ solar, they tend to chip away at existing infrastructure instead of completely replacing plants.

The desert has the benefit that solar can be really well calculated

Oh yeah, solar is incredibly effective here, the main problem is storage. Hydro isn't really a thing since our dams are intended to keep water for summer use, and they refill when we'd want to be generating power. Warm water also isn't feasible at scale, and promising technologies still aren't proven. I'm especially interested in hydrogen storage, since it could be really useful for long-haul trucking (we're a pretty big hub for that) in addition to storage for winter generation.

I was interested in EVs being used for overnight power storage (basically recharge during the day while at work), but it seems like that hasn't materialized.

centralized heating that provides for a whole city block

I don't think we'd need to go that far, putting in buried heat exchangers on new construction isn't that expensive, and I'd expect coordinating billing and whatnot would be more annoying than it's worth (need an HOA, and HOAs can really suck).

The better option, IMO, is to create mixed-use zoning near transit hubs, which would encourage use of mass transit and allow for those economies of scale you're talking about without annoying planned communities w/ HOAs (i.e. business below you could pay your heating/cooling bill). Maybe that's what you were getting at, my point is that it doesn't make as much sense for residential areas IMO, but it could make sense for mixed zoning areas.

I do want to point out that I'm not obsessed w/ nuclear or anything, I just think it's a good option to replace existing base-load plants running on coal and natural gas.