I think a possible mechanic of how they could change it already exists. PvP drops combat, and hence allows you to drink, after 5 seconds of no active role in the combat. What if they reduced the power of the passive regen stats, and instead allowed you to drink after a certain time (not necessarily 5 seconds) in PvE too?

I think if fights were balanced around it, it could be workable. After all, taking a break from healing for a period of time (waiting to flag you as OK to drink plus time spent drinking) is not without cost. It's a reasonable tradeoff, where you probably have to coordinate with other healers when you're going to do it so someone picks up the slack. And if you take damage just before you were about to drink, it was all for nothing.

Well, in raid content most encounters that would be trivialized by stacking healers if they could drink in combat would already be trivialized by stacking healers if they couldn't. Bear boss, for example, would be really easy with 2 tanks, 1 DPS, and 7 healers (would take forever though). I think every other boss in ZA has an enrage mechanic of some kind however, so they would all be impossible.

It is probably a greater concern in 5-person content both because there tend not to be any enrages and because drinking is a greater advantage to undergeared healers (since a t6-geared druid or priest probably regenerates more mana standing around than healer in dungeon blues gains drinking... though of course drinking stacks with spirit regen so the t6-geared player would still gain an advantage from it). 5-person content is already so easy though, it doesn't strike me as a big deal.

I don't really know as it's necessary though. I kind of think it should be possible to run oom and then be helpless. The mana bar is much more interesting to me when there are consequences for squandering it. (Having to sit down and drink is, of course, a consequence, just a lesser one.)

Actually, now that I consider it, one thing this would do is help the mp5-based healers (paladins and shamans) to catch up to the spirit-based healers a bit on fights with gaps in the action (Illidan being the prime example, though outside of maybe p2 I don't think anyone really has mana issues on Illidan), which would be a good thing I think.

When you think about it, the only functional difference between waiting 5 seconds to have to drink, and the current 5-second out-of-casting rule, is that you have to stand still. It's not an exciting mechanic, nor is it strategically very different than the regen boost you already get for not casting (even non-SPT classes, post-2.4).

Quite an understatement.

Stopping casting to regain mana is already a strategic ploy available in game. Adding additional restrictions to this mechanic change it in a way that, while not trivial, also don't improve the game. Not playing your character is generally not an exciting strategic alternative. I have a stronger attitude about that than most, in that I refuse to play classes that have downtime (I've softened enough in recent years to allow bandages). But when the most important and optimal decision about playing your character involves getting up and making a sandwich, you have a flawed game mechanic.

(Yes, I also think drinking in arenas is borderline retarded, although that's a separate discussion)

It's certainly a more interesting mechanic to me than watching a little number of water shield charges and refreshing it before they run out, which is where shamans are at now.

I have no problem with spending periods of a raid fight "not playing my character". To use to overdone raiding is a team sport analogy, in team sports you generally have your players spend some time out of the action to get some rest. And just like in sport, you have situations where sometimes its best to have your players not go flat out in the interests of keeping them out there longer (eg downranking, stopcasting)

Tradeoffs and strategy are for more interesting to me than the actual mashing of keys.

To be able to have periods where a healer doesn't need to heal (=can drink) would generally require more healers in the raid or fights particularly designed to give them a break.

Blizzard could, of course, attempt to design fights where less healers are required, but it doesn't look like they've been particularly good with that in the past.

In addition there are many fights where finding the time to drink would be downright trivial (felmyst phase change for one) while in others fights it just boils down to luck of not getting any damage (m'uru for example).

I think mana mechanics have gone to a better direction of late. There is still some need for tweaking and adjustment certainly, but sweeping changes are not needed.