The question is whether something belong in the language or in a library (possibly the standard library).

A guiding principle of C++ is that if something can be implemented cleanly and efficiently in a library, the language should not be extended to support the use case.

Now boost.pfr is exceedingly clever, but relying on speculative pack expansions or using stateful metaprogramming hacks is not something I would call clean and efficient, so proper reflection is warranted.

I do worry about the compile time impact though.