Which is great and fine as no-one else will be writing software for that particular hardware. I believe that ARM has been allowing some extensions for their M s

Which is great and fine as no-one else will be writing software for that particular hardware. I believe that ARM has been allowing some extensions for their M series designs in these circumstances - partly due to pressure from RISC-V alternatives. I should add that I think that it's possible that Nvidia/ARM combination will remove ARMs 'level playing field' and we might see Nvidia only extensions for their designs - which would not be good. We'll have to see.