We already know you can use individual atoms as transistors [1]. So, clearly we can go a lot smaller than 5mm here. Obviously there are challenges in scaling these new substrates up to create useful chips, and creating the infrastructure to put them into mass production. My point is that we know this is possible, and an inflection point will come where investing in these new substrates starts being more lucrative than trying to squeeze more out of silicon.

[1] https://www.sciencedaily.com/releases/2018/08/180816101939.h...