Sorry for the delay in responding. This PEP had slipped my mind (so thanks for the reminder you added in a different thread!).
I’m pleased to say that PEP 808 is now formally accepted. Congratulations, and thanks to everyone who participated in the discussions.
There is one relatively minor point that should be clarified when transferring the specification into the official standards documentation. The PEP states:
If a field is present in both places, then the build backend is allowed to insert entries into the list or table, but not remove entries, reorder entries, or modify the entries.
This does not put any restrictions on where entries may be inserted - at the start, at the end, or in the middle. In practice, none of the existing fields affected by this PEP assign any meaning to ordering, so this doesn’t matter, but in order to avoid confusion should a future PEP add an order-dependent field, the specification should be explicit. Allowing insertions either anywhere, or just at the end, is fine with me - I’ll leave it to the PEP author to choose.