For a scenario, absolutely. For GT... maybe.

It sounds like you're basically talking about a normal Core + Support structure but the Core would be defined as a cluster of pre-set formations rather than on a per-formation basis. If that's the case, it's going to depend on how versatile the "Big Block Core" is and how much the overall force could be customized. I think something under 1500 points would work better. You might be able to achieve a similar narrow range of flavor/feel and still allow more player selection if you broke it up.

So, if your background was "the dreaded aliens' military doctrine always revolves around infantry" you might have something like...

Core Operational Units
Infantry Horde - 3 formations - 750 points
Reinforced Infantry - 2 formations + 2 upgrades - 600 points
Mechanized Infantry - 2 formations w/ transports - 800 points

Up to 2 Support per Core
...

I think it would be cool if you could add in other units that are not normally allowed in a particular formation to those core formations. Kinda like little 40K armies. Then add in your detachments/troupes/whatever. Of course it would be hard to maximize the potential of a particular formation that isn't specialized in performing a specific role, but it might be an interesting way to play the game.

Just thinking out loud..so to speak.

_________________
-Malakai

"You'll never understand how much watching other people's pain gets me off, hearing their screams and knowing that I have the power of a god." -Velvet Acid Christ