There won't be any wide-reaching resolution upgrade after HD/BD. The technology exists now--there are 4K projectors. The problem is that it outstrips the limits of what the human eye can resolve. When you are dealing with a 36" monitor (sort of the "average" size now?), there simply isn't detail that the human eye can easily measure at such low screen size. You'd have to take a magnifying glass to see the difference.

On a large screen--not a 48" screen but like a fifteen-foot-wide projection screen--you may notice an improvement, but it won't significant enough to upgrade. Only theatre owners will benefit from 4K and even now a lot just stick with HD and 2K projectors because they can't see the expense in getting 4K ones, which have existed for some time. I think eventually all theatres will have one 4K (and maybe in some decades 8K?) deluxe screen for large-format stuff like IMAX or whatever becomes it's equivalent, but I just can't see anyone putting that in their homes. It would be a waste of money.