I have head that molten salt is much safer but also more expensive. Would there be a reason not to go with molten salt?
Meanwhile that same money would buy loads more power in solar/wind and batteries, which are proven technologies that are getting progressively cheaper.
An alternate timeline where we do MSRs in the 1950s and phase out coal by 1990 would have been possible but we didn’t do that and there are better alternatives now.
I have not seen any evidence that solar+wind will provide a proper base load of electricity, and it looks like MSR and its variants will give people the electricity they need.
Every non fossil source except hydro requires a large build out of grid scale storage.
It's true that MSR and Breeder reactors have lots of potential benefits over traditional LWRs but the truth is, LWRs are more than good enough for right now and we literally can't build enough of them if even if we tried.
You wouldn't want to power all of human society off of LWRs simply because they only access ~5% of the energy in the fuel. But we're so far away from that being a constraint. Build LWRs today and keep developing Breeder/MSR tech.