Frankly, this is a good idea. The packaging afforded by the Lambda platform is vastly superior to what the GMT900 trucks offer. Remember that in the latter, the 3rd row is bolted to the cargo floor, it doesn't fold flat, and it's generally uncomfortable. The Lambda solves that instantly, and is better suited for what's positioned as a luxury vehicle anyway. Ride quality would be much better, and if GM Design were to deliver an interior on par with what's now found in the CTS, a Lambda-based Escalade would probably represent a quantum leap forward in terms of styling and refinement over the current vehicle.
As for the Avalanche-based Escalade EXT, MT says that GM's mulling over the idea of moving to a unibody pickup, a la the Zeta-based GMC Denali XT concept, to replace both of those vehicles. Again, not a bad idea, especially for Cadillac. The downside is that owners of the current vehicles who use them to tow will likely need to look elsewhere to fill that need. Still, if Cadillac's gig is to sell legit luxury vehicles, moving to more car-like platforms makes all kinds of sense. It's going to be really interesting to see if any of this stuff actually pans out.