> provided they are even allowed to run their own software on the thing to begin with (which was not the case with Surface RT anyway, extended ISA or not).
Surface RT allowed Windows Store apps, including native ones.
I think you're agreeing with GP -- it only allowed software signed by Microsoft (in other words, you couldn't run your own software or operating system unless Microsoft said so).
In this hypothetical proprietary RISV-V scenario, you might not even be able to run unsigned code on the device and so nobody is going to bother supporting its weird instruction set.
Surface RT allowed Windows Store apps, including native ones.