It all depends on the WHM overall changes; if they make it BLM-ish with slowcast but incredible DPS and healing output (and healing that's not too relying on GCD, or if GCD healing on WHM is made less punishing in terms of raid contribution), Presencoe of Mind can keep that effect of Haste, although I could do with its CD reduced to like 90seconds or 120. It could work like BLM Triple Cast, making all spells instant for some duration.
It could also change the way some spells work, it could be a Mind buff, and it could be a raid buff too.

I always thought Presence of Mind came so awkwardly early in WHM's kit (level 30 I think?), at a time where you are still learning how to heal efficiently (especially if WHM is your first healer), and you won't make good use of PoM before a long time.