The author talks about the code bloat, beacause of "an API that encourages custom formatter specification to live in a template". But at the end he mentions the standard solution to this problem:

> A preferable interface (I use, but also others AFAIK) is to check the type in a template (no choice there), and dispatch the formatting routine to somewhere that lives in a single translation unit.

So what prevents you from doing this with <format>? As I understand, the implementations of parse() and format() of std::formatter don't depend on the template parameters and can delegate to non-template functions residing in one CPP file. You can also provide additional wformat_parse_context/wformat_context overloads if you need wchar_t support.