I ran into this recently writing some C++20 coroutines. The protocol for delivering values from a coroutine that was previously suspended has two flavors: one for values and one for void. My initial draft just implemented the value version and used a struct VoidTODO {} where void should be.

It's too late now. void pointers are used as a pun to mean "type wildcard." If void were a real thing that could have a size and address, that wouldn't work anymore.