Why not use an empty function body?
Then you don't get compile errors or warnings?
Or you want a warning?
Then why isn't static code analysis enough?
If only the "proposal" had some motivation stating what it's for, and why
conditional_t<some_constant0, Some type, Some other type>
isn't usable.
We should all just ignore this unmotivated garbage, there's too much traffic on this list that isn't about serious proposals.