B/X Known World
You can do that anyway. There are a lot of people producing compatible materials for various games and no one gets sued over it. Unless you make stuff compatible with GW games.The fun thing about going this route is that you could then slap "Compatible with Dungeons and Dragons" on the cover and Wizards would have no way to stop you.
Aside from the benefit to creators of being able to openly advertise this, it would be deeply satisfying to see Wizards ending up with less control of their brand.