Is interoperability a requirement for all RISC-V implementations? I thought one of the draws for RISC-V was that adding custom instructions doesn't require an architecture license.
Standard operating system, standard binary-distributed software packages, your own programs compiled with standard compilers with default options, will always run on all RISC-V implementations, forever.
Of course if you go out of your way to use your current vendor's custom instructions (if any) then you're trading short term gain (possibly) for long term pain if you ever want to move on. Always make sure you also have a generic version of that code that runs on standard chips (if not other ISAs too).