Yes, in practice the only things that really need "porting" to POWER are low-level compilers, languages, runtimes, tooling, etc. that may have arch-specific cod

Yes, in practice the only things that really need "porting" to POWER are low-level compilers, languages, runtimes, tooling, etc. that may have arch-specific code. Sometimes IBM does this (e.g. Google v8 + Node.js), sometimes not... yet? (e.g. rust).