There is a reason TSMC is the only fab working on <='7nm' class lithography. It is hard. It also requires massive amounts of capital expenditure. And that's the case when the critical equipment is bought from a different company that's again, in a league of its own.

So even if the 'only' problem is putting the pieces together, that doesn't mean it is even possible. Look at it another way-- same thing can be said about Nuclear Fusion :D