Except for loss of economies of scale. Semiconductor fabs and nuclear reactors are just about tied for the most expensive industrial plants you can build.

It is not clear whether Russia is in fact planning to build its own top-notch (28 nm, 16 nm) semiconductor fabs. I assume they won't, at least not at first. Building "your own" ARM processors based on stock IP cores licensed from ARM Holdings and fabricating them on commercially available foundries in Europe or China looks like a reasonable way to escape the US-based Intel and AMD and should not be ridiculously expensive.

How would you know the IP cores are not backdored or the fab is not inserting flaws that cause backdoors[1]?

1 - http://sharps.org/wp-content/uploads/BECKER-CHES.pdf

IP cores are just source, right? With fabs, you at least have some choice.

I know almost nothing about this, but:

(1) IP cores can be bought as "binaries with API", not as source. This is cheaper, but much harder to inspect.

(2) I think that "compiling"[1] the source to some fab's process is not completely automatic (they "recompile" or "handcode" some "functions" to optimize power usage or max frequency), so you need to verify the "binary" is faithful to your source, including on the analog level. Then you need to verify the manufactured chip is faithful to the tape out[2] you verified, as a 3d apparatus, not just the xray.

1 - https://en.wikipedia.org/wiki/Place_and_route

2 - https://en.wikipedia.org/wiki/Tape-out