I think this could prove done very interesting changes that actually means your spec will change as your gear up.
For example holy pala's I'd guess the mastery stat would be some form of healing bonus and that retris would be some form of crit bonus on casts/spells.
As such when u originally hit 85 u maybe need more of the retri spec to keep crit high and thus get more mana back (blizz have already pretty much guarenteed a rape to our endless mana - and rightly so).
But as you get higher gear and higher stats off it you won't need the crit anymore so can dive further into holy for some massively high healing or into prot for some form of damage mitigation for raid (how I imagine prot mastery stat).
I could be way off - but either the possibilities are far more exciting than when wotlk arrived.
I do worry for some crazy pvp specs tho (for instance the old OP prot holy spec) if blizzard don't keep a close eye on the possible hybridization.
To stormgust: I really hope you are wrong on the pala HoT. If they do give us a decent hot (and the current flash the shieldy hot is crap) they will be slowly giving all classes all forms of spells which blizzard said they were trying to steer away from. Ergo I rolled pala not tree / priest.