When transistors stop shrinking- whether that's at 10, 5 or 7nm- the limit is going to be economic, not physical. Intel probably could make a chip with 1nm transistors; the question is whether it would ever deliver a positive ROI, since

- the R&D and the fabs would probably cost a zillion dollars, in a shrinking market for high-performance CPUs

- yields would probably be very low, even as the process matured - this problem is becoming more and more pronounced with the latest generations

- the advantages over the current chips would not be great; note svantana's comment about diminishing returns with the most recent process shrink