although for these PODs it won't matter, consider using direct list initialization, since in-class assignment might make copies

no need to delegate to CBlockIndex() since it doesn't do anything. Rather you could also use an initializer list instead of assignment in the constructor body.

I'd rather ensure that the types are movable if need be.

Keeping the code similar to upstream is a feature, IMO. Plus I'm fairly confident the codegen won't be any different considering this is just copying a few ints around under the hood.

TIL initializer lists aren't movable :/

Is it possible to statically assert that CBlockIndex IS movable? Otherwise regressing on this to match upstream appears imminent.