Its an interesting concept with its own pros and cons. Bright side the resto 4 piece (in which rejuv gets stronger with each tick) - will lead to a lot more overhealing (except on a constant damage fight like garalon) - which in turn will charge the shrooms faster.
Kinda skimmed some of the math/mechanics posts but shroom healing is capped at 6 targets for max value and then divided by # of targets healed, just like healing rain and sanctuary. IIRC.
Certainly gives some options of using them right away after you place them for small healing (standard as now) or letting them sit for larger burst after a min or 2. Optimistic, but waiting to see more balance and number run throughs on ptr before i cheer or jeer.