Mainly just a case of developing the design. If you know how to get performance out of a processor then the instruction set is largely secondary. However, a high performance processor is not a simple thing to design.

That’s not to say the other factors you list aren’t an issue. The latest manufacturing processes are only available from TSMC and all production slots are bought out by nVidia, AMD and Apple. Everybody else has to make do with older processes.

Adoption is probably the easiest one. Linux support for RISC-V is pretty good and recompiling software for it is pretty simple.