OK, sorry. .pyXY-none-any. Or we could update the wheel spec to have a way to explicitly say “contains no built artifacts”.
This is why debating whether wheels are binaries or not is futile 
Going back to an earlier point you made
… and that’s where (something like) --no-binary :all: makes sense.
Is anyone here (apart from @pganssle, who has made his position pretty clear) arguing for a solution that requires frontends to use pre-built wheels at some point in the PEP 517 build chain, in order to support self-hosting backends?
If not, then can we discard that option1, and return to looking at ways to allow self-hosting backends to express how they should be built? (And to keep the discussion concrete, can I suggest that we also accompany each proposal with a description of how setuptools would be specified in that proposal?)
1 I’m not ignoring @pganssle’s points, I just don’t think endlessly rehashing the discussion in an attempt to persuade one person is a good use of our time. Better to explore alternative options.