Allow me to rephrase myself, "how do you move the cab forward if its already up against a wall preventing it from being tilt back until its moved away from the wall?"
To do that you have to drag it on the floor to slide it out from the wall before tilting it back. It's not as bad as it sounds unless you're doing it on hardwood floors. Then there might be some scratches left in the floor.
I always liked the cabs where the manufacturers were thoughtful enough to add the "dolly wheels" (as I like to call them). Most of the big manufacturers did this. If I were scratch-building a cab I'd probably try to utilize casters this way. But considering my carpentry skills and the cost of buying an existing cab, I'll probably never scratch-build a cab.
I think you should definitely reconsider the swivel casters. Think of it this way--once it's done, how often is it going to need to move? In the end you'll want it to be a big, heavy, rock-solid monolith of gaming. At least stick to straight casters that preferably have a locking mechanism.