I find the Mudra system irritating on the best of days. I don't think that Mixing should involve pressing multiple buttons to perform one action.

I'm looking for something that is both intuitive but also has some room for strategic thinking. Throw a potion on someone, give them a HoT effect. Throw a second potion with it active to turn it into some burst healing or an AoE. The 'Mix' involves building off of the buffs/debuffs that you've already placed on players or mobs. With correct planning, you should be able to setup an effect that you can take advantage 10 or 20 seconds down the line.

Remember that the charge system applies to cooldown-based abilities, not GCD spells. Most of the interesting action on healers happens in-between GCDs. I'd like to see a system which acknowledges that fact. So you weave in a healing potion in between whatever filler GCD set you use at baseline. Great. Now you have an extra charge of a damage ability that you can weave in later on as well.

By 'WHM-like', I don't want to see a 2s cast "Potion" which costs 1000 MP. You could expand the existing Lily system into something similar to what I was suggesting, but it would require rebuilding WHM from the ground up.