Blood elves and Nightborne would be nice to get a botanist druid sort of vibe, more about the arcane parts of druidism.
We have seen orc druids on Draenor (well at least one) and broken druids on outland so those would be nice. The undead could probably be druids if they were risen kultirans. Pandaren are descendents of the bear loa, strange they aren’t druids.
I think mechagnomes should be able to shapeshift, and call themselves druids. I mean think of it like transformers beast wars more so than traditional druidism. They already have some models in game too. mechanical cat mount (cat form), That mechanical parrot (flying form). Mechanical Bunny (travelform). Robotic Gorilla (bear form). Rocket Chicken (boomkin? lol)
I mean they could get really creative and have fun with this race and its forms.