After using the current system for a few days now, I do have one area of concern with the lack of medding during combat.
This has to do with the fact that if a pull goes bad or there are unexpected adds during the fight, the opions become very limited now. Especially if your mana users are LOM after an extended fight and a mob(s) is aggroed. For the most part (not totally) helpless. You pretty much die, with no chance of getting out of it.
Before, your tank could hold it long for someone to squeeze off one last root, giving the group enough time to recoup just enough to finish it off. Or perhaps everyone is OOM but there are still a couple of mobs left. With in combat medding, there was a chance (even if it was small) that you could pull it off and come out alive. Currently, there is no hope. So what if you manage to park them, now you simply wait to die.
With and without combating med when it came down to a rough fight, in both cases you pretty much have X number of resources to work with. With combat med, when those resources run out you were given a tough situation and you have to figure out "we're screwed, now how the hell do we get out of this?". Without combat med, when those resources run out you pretty much say "we're screwed, i hope the cleric can camp in time". And for me this causes one of the most fun things about this game to be lost.
One suggestion i can think of is maybe trying to balance out and in/out combat medding a little in the opposite to what it is now. Perhaps speed up in combat med, maybe not exactly where it was, but a little closer to it. And slow out of combat med back some. Maybe by doing this it will provide the decrease in downtime and sitting that is required for mana users, but yet still give a group a fighting chance, should the situation go bad.
Just for reference I am looking at this from a lvl 60 cleric and most combat has been XP grouping. So far with the new system I have not done any raid situations so I don't pressume to know how that part of the game is affected.