I'm pretty sure that's not going to be "the shortest route," J, but it may be "a route" eventually. Samsung already produces a NAND flash chip at 10 nm. The lattice spacing in crystalline Si is about 0.54 nm, so we're talking about a transistor feature size of a bit more than 18 atoms. These are available on the market as we speak, and you might even be using one right now if you have a sweet new Samsung SSD.

Proof-of-concept Si FETs have been made down to around 3 nm, last time I checked, or around 6 atoms. Grossly speaking, these are essentially refinements of photolithographic CMOS processes. Soon we'll hit a wall with this, but for now, I think atomically-precise manufacturing is already pretty achievable without engineering biology.