Hardware revisions, yes, as said, updating screens and the insides of the 3DS, surely that will happen. Major form redesigns though, probably would come, but as said, can't be anytime soon. A "Lite" is undesirable right now, as it is portable enough being based on the DS Lite form-factor. They would probably do it to extend the life of the 3DS, as with the "updated" DSi, which I skipped for the "dying" DS Lite. I think Nintendo should play it out a couple or so years and see what they really need to change, chuck that out and make more $$$. In the end it's all business. If a major redesign is the best move in some time, and when components get even cheaper for better performance, what's to stop them from incorporating those?
As with general consensus, I'd prefer an "XL" type of revision. Sure it's not very "portable" but it is still a handheld, which I would be great for some people's lifestyle.