The gestalt rules my face-to-face game is using are:
Choose two classes (you can still multi into one more if desired)
Gain 4 class abilities (or all of one class's if you choose all four from the same class.)
Gain an extra At-will, encounter, daily and utility that can be retrained as you advance.
Take the best of class saves and hit points.
So far it is working well. I would strongly advise against giving characters all the class abilities of each class. With 4 choices, you have to make some hard choices, ad you cannot do it all.
As for the topic, I hope to see some dual-classing coming up. The system allows for it easily, perhaps taking all of your powers as, say fighter, until level 5, and then starting to choose from warden, or retrain out fighter powers at higher levels.
It could work pretty easily.