I'm sure a 4.0 will be around eventually for it. I've had a lot of fun with Cyanogenmod on an NC. The only con possibly being that they didn't hook up the BT antenna in the thing or something, but you can get an earpiece bound to it from like 6 inches away (now that's some near-field communication!)
I'll add the bigger problem with CM7 is the battery. My factory Nook Color could go a week or two between charges. Picking it up and just reading a book or browsing was never a concern. Now that I'm on CM7 there is a 50% chance the battery will be totally flat when I go to pick it up.
Realistically, it doesn't matter, since even if it did run 4.0, all of the shiny new interface of 4.0 will be nowhere to be seen. Android is the base, but nearly the whole GUI is custom. And I believe the Nook Tablet is based on 2.3. The Kindle Fire is based on 2.2.
IIRC the Color runs 2.2; so I'd expect at least that. Odds are it'll be 2.3; they've had the time to work with it. Even Google's "core partners" (Moto, HTC) are claiming 2012 for ICS updates for their handsets, and they're probably getting advance access vs. B&N.
"They've had the time to work with it" doesn't register. Amazon has been a software company from its inception and has had a substantial team of talented devs working on the kindle and kindle fire projects. B&N has never been a software company, it's a functionality they've bolted on to their company lately, and we have yet to see how good that team actually is.