If I had brand loyalty I'd be driving a Jeep. No brand is perfect, no vehicle has a perfect record with zero issues. Companies are in it for the money, everything is a compromise. However, I do think GM is actually pretty good. High end sports car - one of the Corvette variations would be my top choice, new SUV - a Tahoe, hybrid - without a doubt the Volt is the only hybrid I'd consider, muscle car - Camaro. Their economy, sedan, etc. offerings are pretty boring and I doubt I'd choose a GM.
Point is, GM can build a good vehicle and if they do come out with a real off road vehicle how good it is will depend on what they think the market will bear and what price point they make compromises to hit. It's not a question of if they CAN build a great vehicle, it's a question of if they will.
To the issue of GM abandoning Hummer owners, that seems to be a question of which dealership you go to. The Cadillac dealership I was going to for factory warranty work was great. No questions asked, loaner cars, full vehicle inspection looking for other parts that may need replaced.