Aspect of the viper (which will be trainable at level 20 I believe) will no longer grant MP/5 based on a percentage of your mana, but will reduce your damage done by 50% and cause you to regenerate mana equal to 100% of your damage caused (via an 11-point BM talent, you can decrease the damage penalty by 10%). Under this system, for about every 0.4 DPS you do, you will get 1 mp/5 (so for 2000 DPS, which shouldn't be too hard to achieve in LK, you could restore a 10k mana pool in 10 seconds, at the cost of 10k damage or 1k DPS).
I like this, since it will actually scale with our gear (intellect would stay about the same as hunters get geared, but the other stats go up faster) and it allows us a huge burst of mana back (at a cost) before we switch back to hawk/beast (beast if your pet is tanking).