Use achievement points to unlock perks -> for example 1k achievement points unlocks a class at lvl 90.
When you create a lvl 90 character, it puts you in a solo dungeon (scenario) that teaches you the basics of the 3 specs. This should take a while to get through.
At the end you choose 2 specs and get appropriate green leveling gear for them.
Other perks can include race/class combination unlocks (250-500 points?), automatic mount skill unlocks on new characters.
Some of these should require achievements. (for example mount skill unlock requires that mount skill on a certain character)
Since this would require players to get more achievement points, make dailies, dungeons, raids give achievement points (GW2 style)