Since the "nm" numbers are just marketing anyway, I think they don't mean much in regards to how small we can go. We can go small until the actual smallest feature size hits physical limitations, which is so decoupled from the nm number that we can't possibly tell how close "7nm" is (well, I mean, we can, there's a cool youtube video showing the transistors and measuring feature size with a scanning electron microscope, but I mean we can't tell just from the naming/marketing).