That does sound really cool! But how would it work in a sort of triage environment? Like in a 5 man when s**t hits the fan, or in a raid with constant damage? How would haste effect? I wonder if you could even get to a point with the right stats where spamming the fast heals is often enough and strong enough to make the larger charged ones unnecessary. Would you be able to charge for a large period of time before some raidwide aoe and use that as a sort of huge healbomb cd? Can you charge while moving?
One idea I had was implementing a secondary resource (like how Holy Paladins have Holy Power or Mistweaver Monks have Chi) that increases when you "charge" your spell, and you gain one full charge after you charged for a certain amount of time. Think of how Destruction Warlocks and their Ember resource works.
For example, let's say this resource stacked to 100, and every 20 of this resource was divided into a full charge, or 20/20/20/20/20. Every 0.10 seconds you spend "charging up" a spell would grant 1 of this resource, so charging up a spell for 3 seconds would grant you 30 of this resource. You could then spend full charges of this resource (such as 2 full charges, or 40 total resource) on a more powerful healing spell, such as a large tank healing ability (Word of Glory, Enveloping Mist) or a more powerful raid healing tool. (Light of Dawn, Uplift) This way, you could spend lull moments in healing charging up your resource with these charge-based spells and unleashing them when those "oh shi-" moments arise.
There could also be more expensive baseline spells that grant more of this resource (such as 2 every 0.10 seconds of casting [for 20 resources every second of charging the spell] but the mana cost of the spell increases in relation instead of decreasing). This would act as the "emergency heal" ability in the toolkit.
Haste effects won't affect the charge-up time in any way, but would reduce the time in-between resource gains when charging up a spell. For example, at 0% haste, you would gain 1 resource every 0.10 seconds of casting, but at 25% haste, you would gain 1 resource every 0.075% seconds spent charging, or 50% haste would yield 1 resource every 0.05 seconds spent charging. The rate at which healing would increase and the mana cost would increase/decrease would also vary depending on haste.
Charging-while-moving could be a specific ability that trades healing ramp-up/mana efficiency for the ability to cast while moving.
I really really love getting all brainstormy about things like this! I used to try making custom DnD classes as well but getting a DM that actually will let you play one..... :/ well let's just say I had alot of papers collecting dust.
I really hope devs read things like this. After all Blizz wants to make money and the number one rule is give the customer what they want, right? Take our ideas and RUN with them so to speak. Sort of sad how WoW is starting to die though. I guess most mmos have their time....
It's good to be open-minded about new ideas and class designs, which is why I like spending a lot of time myself brainstorming these sort of things.