Considering the time between the artificer's preview article and the Eberon book dropping, I wouldn't be suprised if MPII ended up coming out after PHBIII, and the 2010 setting, which would definitely give it a lot of races to have paragon path/feats for, if nothing else. And, if it's after Adventurer's Vault 2, that would also mean perhaps some new weaponry to build around, etc.
EDIT:
From the previous poster ... PHBIII would either contain some old power sources, or two new ones. Since there are 4 power sources left (Ki, Shadow, Psionic, Elemental), it's quite possible that they go with 4/4 for new classes. Ki + Psionic might fit, as they have a mind/body concept that is similar to martial/magic or nature/magic from the previous books in terms of split. While shadow would fit as a "ninja" power source to compare to ki, I would think that shadow and elemental being paired might seem more appropriate as they both draw power from a location (shadowfell/elemental chaos) as opposed to the 'internal' power source of ki/psi.
Long story short, it's possible that they have 2 new power sources in PHBIII, and thus, two new "power" books to put out. Also, once they have Martial Power II, Arcane, Divine and Primal II can't be far behind, etc.