varying regeneration rates?

In WoW mana and health regenerate at a constant rate for a character. That constant rate might be different from other characters, but constant for that character .. unless of course they buff themselves, swap equipment, eat, or otherwise change the exact character context. Thus, if for a given character the only thing changing is the passage of then time their regeneration rates are constant.

The one exception that comes to mind is with hunters and their Aspect of the Viper: with that buff, their mana regenerates faster when they are low in mana, and slower as their mana pool refills. It's thus tactical to switch Aspects depending on your current mana pool and requirements - it's better to run your mana almost right down, pop Aspect of the Viper, hit Rapid Fire, Bestial Determination, and whatever haste trinket you have, and then sit back just auto-shotting while the 5 second rule works to your advantage. Wait until your mana pool has filled up some, and your rapid fire and haste buffs fade, and then and only then quaff a mana potion to top up.

This situational awareness tactical element makes playing a hunter more fun.

Some other classes have their own buffs for increasing their mana regeneration rate, but as far as I know none of those vary according to what your current mana level is.

Apart from passive regeneration, mana can also be regenerated by eating, drinking, and quaffing potions. While most potions have an instant effect, some potions restore mana over time. This presents another opportunity for playing with the mechanics - who says the mana per second from drinking is the same at the beginning of the drink as from the end of the drink? The PTR for patch 2.4 is playing with this mechanic. Players don't like it, although it may not be so bad as the flood of QQ suggests.

So .. what if there were other ways the regeneration rates could vary? What if the base regeneration rate itself varied according to fullness (but opposite to the Aspect of the Viper buff above). As a thought experiment, what are the upsides and downsides of a system where regeneration was much faster for the top 50%, but much slower for the bottom 50%? What if the faster regeneration rate only kicks in if you are sitting or walking (ie. not running)?

Reading that PTR 2.4 thread clearly indicates that varying the regen rate would have an effect on tactical flow: at one extreme players would constantly top themselves up and keep moving, while at the other extreme they would go all out, exhaust themselves, and then camp to recover. I've always thought the latter pattern to be unrealistic and immersion breaking - why they heck doesn't that next set of mobs just over there not notice that we've slaughtered their comrades, and why do they not wander over while we're all sitting down chugging down drinks and food?