Prior to P2587 I'd say that the two main issues with using std::to_string are that better options are available in charconv; and the locale and other issues laid out in the paper. It seems that the adoption of the paper resolves both those issues.

I'd be in favor of keeping std::to_string around though. Primarily for a code semantic purpose - `auto x = std::to_string(1234)` is simple, readable, and tells you exactly what you're getting. Whereas `auto x = std::format("{}",1234)` is just one step detached and requires a little extra brainpower to process. And of course in the case of widestrings, the requirement to prepend your "{}" with an L only adds room for silly mistakes to be made.

There are also the possible concerns re code size and linking to all of format which have been previously mentioned.