It's hard to speculate on this sort of thing. Die-shrinks can happen, but I think there will be a point when the physical die is too large to remain efficient (could be too power-hungry). GPUs get away with having hundreds of cores because they are mostly fixed-function and have nowhere near the capabilities of an actual CPU core.
I think Intel could continue to add in more cores as the die-shrink decreases, but I think what it's doing now is just focusing on overall performance of each core (a lot of people don't -need- a million cores) and possibly adding in extra silicon for specific tasks (instruction sets).
I don't really see 10-cores on the desktop happening for a while, though it's hard to say. We -will- see eight cores next year, and servers already have 10-cores. I know I'd not turn down a 10-core! On the six-core i7-990X it takes about 8 hours for me to transcode a Blu-ray into an archival 1080p video. Almost makes me want to build a Xeon dual-socket server