I don't have Outland experience on a Druid yet, but yesterday I helped a former guildie of mine in Ramparts with my 64 Pally. We had three 64-65 with good gear and two 60-61 who pretty much just got in Outland.
Nevertheless, just with us three 64-65 we could've trio'd the instance, save for a few bad pulls. So with 3 Druids at 70 it's entirely possible. I've ran Blood Furnace, Slave Pens and Underbog so far. The two latters were much harder cause finding a good PUG is nearly impossible lately. Eventually did UB but SP remains unfinished and every time I ran either of these we had someone who was 68-69 so it should've been much easier. Yet, it wasn't.
Sooo, maybe at 70, once you got some awesome gear, trio'ing instances is possible. Or maybe full stealth run 3 Druids + 2 Rogues. I'm curious to find out which bosses are soloable, if any.
I miss you Smolderweb. :(