Smite healing hasn't caused this, and I don't recall stacking shadow priest has ever been a tactic to help healing...

Both shamans and priests have an active "damage to healing/mana regen" ability (those are the only two healing classes I play, so forgive my ignorance), and you don't see raids or five mans stacking them because of it (if I recall, Paragon's world first Sinestra had no shamans at all). Granted, Monks may be doing something similar on a larger scale, but I think it's clear that this model isn't somehow game-breaking or ridiculously OP.

I would guess that Blizz is well-aware of this going into it, and I'd wait until we see some action in the Beta before making judgement.

Just been thinking about this and I've had a couple of thoughts

1) are healing pandas also going to have to be hit capped? Its probably already been answered, but if so then blizzard could probably make them gain hit like a priest does through spirit conversion.

2) you could also stack shadow priests specced into vampiric dominance and do 15% of their dps as healing to 3 people (as an example, 30k dps translates to 13.5k hps over three targets, 4.5k per target).