As a player who loves to try different aspects of my L85s, I feel that it is time for Blizzard to introduce multi-spec: Tri-spec would be a good start, but I don't see why having 4 or 5 would be such a stretch.
My current "main" is a Druid. I have a PvE tank spec and a PvP arena spec. I would love to have a PvE DPS spec. I also have a banked set of random Boomkin gear that I've collected along the way that I would love to try, but I don't feel like respeccing back and forth, both in talents and glyphs at 140g each way, each time. It's not even really about the money - I'd gladly pay 10,000 gold for a third spec - it's about the hassle.
The way I see it - they have implemented the bulk of the programming and game design considerations already. The dual-spec feature is well-engrained into the game, with it's quirks already worked out. Where there are 2 tabs now, there could be 5. It would likely be just a few dozen lines of carefully placed code...
Please bump this thread if you also want to see this seemingly simple idea implemented ASAP!