This is a druid blog, but I did make a mage when I first upgraded to Burning Crusade (BC). They sit soo cute I had to make a Draenei mage. And I love loved frost spec, but it's not good for anything except some pvp. But recently with conquest badge gear being easy to obtain I found that, like when I was level 70 running instances in BC, I could tank pretty well as frost. Not bosses, of course, but any trash is really easy to keep on me and slow it down so it doesn't hit me. So it just makes it seem like a really intriguing concept. They could rework the frost tree so it could be a pvp or tanking spec, and it'd be really interesting I think.
There are some major issues to overcome of course. Gear is one thing that I just don't know how they would do it. Be interesting if they somehow made it all talent based. Somehow make talents convert gear stats to tanking stats. Then of course making a mage tank they'd have to limit the amount of damage the mage could put out while upping survivability. And then this is all just crazy and insane, but some sort of caster bassed tank would be really interesting to me. Everyone else uses weapons, so boring.
Patch 7.2 for balance and resto druids
4 weeks ago