Blizz stated in a watercooler that they're using the 1.12 database as a starting point. I don't think it's a stretch for people to assume that most game features and mechanics will be in their 1.12 state. The kind of stuff I would expect to see reverted would be numerous AV changes, but I seriously doubt class mechanics are going to be reverted. I'd be surprised if the threat changes that ruin pre-naxx encounters are reverted.
Expected More That WoW Classic Will Resurrect That Hardcore Breed Of MMO That So Many Players Originally Fell In Love With. In World Of Warcraft Classic, It's Built Using Patch 1.12, Titled Drums Of War, Released On August 22, 2006, Equipment And Abilities Will Remain Stable In Order To Reflect The Minor Adjustment That Blizzard Made With Each Path While Dungeons, Raids, And PVP Features Will Constantly Change.
I am not, generally speaking, a conflicted or complicated gamer. I do not buy tons of titles. My Steam library is not stuffed with hundreds of games I’ve paid for but never played, apart from the ones I use for benchmarking. Hilariously, this means I have thousands of hours logged in a few games I’ve never actually started, but relatively few that I purchased for the purposes of playing and didn’t play.
So even though you can play a WoW Classic demo today, we’re not done quite yet. We have lots of capital city features to look at, such as banks and auction houses. We need to test our dungeons and raids to make sure the bosses’ abilities all still work correctly. We need to examine all of our PvP systems. But we’re committed to taking a close look at all of these and more as continue bring the classic game back to life.