This could be a pretty decent idea for an alternate game mode. It would be different enough from the usual gameplay style to be an entertaining addition.
However, I think it should have an inbuilt restriction on many troops just to be functional. Skull generators are one thing, but there’s also Entangle, Hunter’s Mark, and many troops who remove, explode, transform or otherwise do anything in relation with Skulls (Frost Giant would be nerfed to death in this mode, for instance).
Most importantly, every single troop would in essence be a Fortress Gate on the board, except for a few specific troops whose Attack value does something else besides determining how much damage they do with skulls. With this in mind, the risk of launching a stalemate game could only be avoided by outright banning troops who don’t do damage with their spells. If you have even one troop who does no damage with its spell, there is always a possibility that you will be literally stuck if it’s the only survivor. No one wants to see two Entangled Fortress Gates fight to the death, as it could only possibly be death by boredom. ^^
PS: Skull-less*. When I first saw the thread’s title, I thought you were asking for “less mini-games”, and that you for whatever reason dubbed this project S.K.U.L.L. ^^ I was puzzled, since we only have 2 mini-games, how someone could possibly complain we have too many already!