Proprietary extensions need to live in the opcode space reserved for custom extensions, where it'll overlap with other vendors' own custom extensions.

If they conflict with RISC-V's own space, the chip can't use RISC-V trademarks.

And, of course, the RISC-V Consortium will never adopt proprietary extensions, as that goes against its core values.

What matters is what is on the market, and how it is made available.

Everything else matters as much as FSF point of view on something being free or not.

That's why there are licenses and agreements.

So that we do not have to rely on anybody's goodwill.

And since RISC-V allows for extensions, all bets are off regarding successful deployments being extension free.

Just like many open core products that really need the full deal for being usable in a proper way.

Expecting otherwise is whishful thinking, or academia/maker community focus.

There already are. As long as they're in custom space, there's no issue.