> Is this going far enough?  What about thousand separators?
> If your locale has / wants them, you need to parse and reallocate
> even with your "new" interface.

The functionality to parse integral, fractional, and exponent parts is already embedded in std::from_chars, and we may as well expose it to the outside. I don't think this is particularly controversial. It would be more controversial to also add novel support for parsing a digit separator of choice. I don't see a strong argument in favor or against it, but a very strong argument to provide a lower-level function in general.

Keep in mind that std::from_chars for integers also draws the line there. Unlike std::from_chars for floats, it doesn't require you to use decorations like "0x". It supports any base, but no separators, and that may be a good point to draw the line.

Also you don't need to reallocate in any case. There is a relatively small upper limit to how many characters a float could need to be represented with no loss of information, although it's not easy to determine that upper bound without pessimizing.