What are the top 1-3 mechanics that you would like to "borrow" from GW2.
1. World vs World. I want massive battles that just continue on almost endlessly that you can hop in and out of with no penalty. Blizzard is most likely not going to return AV to the way it used to be so this would be a possible alternative
2. The Waypoint system: After coming back to wow after playing GW2 i was kind of irritated that i had to run back to a flight point in order to go to a new zone and if my HS was on cd i had to walk.
3. Down scaling of levels. But in dungeons and raids only (maybe a few zones). Maybe have a separate version that you can toggle (like how you toggle heroic/normal) so that technically all dungeon/raid content could be level appropriate. (note: keep a version that does not mess with your stats in case you just want to farm for Transmog
I would take the combat systems as well but that would be too massive of an overhaul to pull off and would make a lot of people butt hurt.