Let's have a discussion about features we'd love to see in-game, without the "but that'd never happen..." Let's just let the ideas flow without the hint of existential misery.
My personal idea is that rock-type would be resistant to ghost and dark, in light of Spiritomb being sealed by a stone, along with other sealing rituals in the real world. This would make fossil pokemon much more viable. Who doesn't love Kabutops and Omastar? Awful people, that's who, and I'd love to see much more of them.