I think the point of this would be to lower the barrier for contribution as much as possible. Requiring a README for /contrib/ is a good idea, but for /works-in-progress/ we shouldn't require anything at all.
I assume there would be a better name for this though, since works-in-progress seems to imply that 1) all the other stuff is finished and 2) it is actually being worked on the stuff in there, but I think a big part of it would be abandoned/partly finished stuff that someone just wants to drop there in case it is useful to anyone else.