I've recently finished Grizzleheim on my fire, and I took a look at Wintertusk. Whoa. It's way beyond Ravenscar and Dragonspyre. The first mobs I saw had twice the health of any other mob I'd had to fight. So do you think that Wintertusk should have a minimum level like the other parts of Grizzleheim, so people don't get overwhelmed?
In my opinion, if you can beat the Coven, you shouldn't have a problem in Wintertusk. Unless you have some level 100 helping you out, in which case you should probably wait to go into Wintertusk.