Regarding parse_float, I fully trust @hukkinj1 to make the right decision. My opinion should be clear now, but I’ll sponsor and support the PEP either way.
OTOH, if anyone wants to add write support now, start by finding another PEP sponsor. As far as I’m concerned, it’s out of the scope of this PEP, and should be discussed separately. I’m not saying it would be bad to add it, just that I can’t commit to helping to add it. (And also, I think the discussion would delay this PEP far too much.)