Chespin will become a Pyshical Tank, so Grass/Steel would be nice... Yet Ferrothorn says Hi! But a Physical Grass/Dark sweeper is highly wanted... But Shiftry... I like the 2nd more.
Just because these type combos have been done before doesn't mean they can't be done again. Swampert was Water/Ground despite Quagsire existing. It is notable that, besides Fire/Fighting being repeated twice(exclusively to starters) and Swampert that it hasn't happened before. Still, I'd like to see a Grass/Steel type as its marginally better defensively than Grass/Dark which has iirc 6 weaknesses.