The Flameward Hippogryph, the flying mount that players can earn after completing their own personal progression through the Regrowth and the Molten Front, will be available to everyone who makes the effort. In addition, players will be able to start the content at level 85 and must have completed the Hyjal questing up until reclaiming the Regrowth area.
Marks of the World Tree, the personal currency being used to open up content in these new daily zones, will not be used to purchase gear and items from vendors. These marks only exist to open up content, not purchase things. Gold is still the currency used to purchase items, and if I wanted to take a guess, I would imagine the cost of items will be similar to those of an already existing Cataclysm reputation vendor. Blizzard has assured players that any marks that they have afterward will be able to be used for rewards as well, but at this time there is no information on what.
Finally, the two new factions that players will be assisting in the Regrowth and the Molten Front, the Druids of the Talon and the Shadow Wardens, will not be receiving their own factions to grind in the patch.