I can't decide if it's worth continuing my work on a PEP. I need
to re-read and consider the various questions and suggestions from
today. Thanks, everyone, for your input.
Even if we decide not to do it, I think it would still be useful to have a PEP with the pros and cons of various design choices written up. Negative results are results too! (I think this was part of the original plan for PEPs, although right now I can't find it in PEP 0.)
F-strings are such a tremendous success that it's inevitable that making them the default will come up again, so the effort of writing up how it could be done and what problems it would encounter won't be a waste.