An open ISA is a good start. It means short of any closed-source extensions the code can move to another chip vendor. With smart modularization of the code, even parts using closed-source extensions could be potentially retargeted faster than moving to a whole new ISA. Finding a radiation hardened complete solution that's totally open source could be a tough request to fill.
I think it's a rather pragmatic decision given corporate capitalism is the economic model under which most processor design and trade happens, at least toward the higher end. The good news is since the main ISA and several open extensions exist, any open source hardware implementation of those aren't hindered by the ISA. That's also true for SPARC, POWER, and a few others of course. But RISC-V seems to be the belle of the ball and apparently simpler to build a hardware design around.
Someone, somewhere may eventually form a coalition to pay TSMC or Samsung to generate an in-house spec for a high-performance RISC-V processor with an open-source license on the hardware design, too. Some places use RISC-V in products where the processor is another line item in the BOM and not the centerpiece of a SOC or dev board, like Western Digital using it in storage products. A group of companies and institutions could very conceivably get things where we'd wish now that the open ISA has set the stage.
> rather pragmatic decision given corporate capitalism
Supporting a system that centralized designs of critical semiconductors in the hands of few companies and manufacturing in the hands of TSMC is not very pragmatic. If anything it's very ideological.
Acknowledging that's the system under which something has happened does not imply, let alone assure, personal support for that system overall. The real world doesn't bow silently in deference to our hopes and dreams.
