There a reason why lilies are used on healing skills only. It's because of how the misery potency lines up with other healers using an ogcd. Basically the potency value of rapture and solace is 225. That's 75 less than glare. This lines up perfectly with the fact that oGCDs also have a cost of about 80 ish potency. This basically means that WHM's "cost" of healing with afflatus is equal to the cost of healing for the other healers. Adding any form of extra potency skill on the lily system would skew it completely as that would mean that healing for WHM is actually a DPS gain so long as you use one dps lily out of the three. This would be terribly broken and also make the whole mechanic lose it's fun factor. Since right now it's a blancing act between using it to heal and using it to weave. That balancing act disapears the second you give WHM a dps lily skill.
With that said I've been an advocate for returning potency on fluid aura (with the 30s cooldown). WHM currently still lacks a dps ogcd and that would be a great way to add to the gameplay. If they could do that and fix the ruin II potency + fairy bugs on sch that would be two healers down and AST to go