The RISC-V is an extensible ISA, so yes. All those vendor extensions are optional, when fabricating the processor, which can be replaced by other extensions over time.

Both Intel and AMD have had vendor extensions in the designs that they no longer use, even ones that have been "retracted" (i.e whatever in the heck Intel is doing with their AVX extensions).

But yeah, currently, there are a lot of proprietary extensions, which could still be declared as open hardware as well. So yeah.