Now it is how it works for embedded processors[1], I see no reason why that can't "tricle up" to the more powerful ones.
[1]: https://techcrunch.com/2019/10/08/arm-brings-custom-instruct...
[1]: https://techcrunch.com/2019/10/08/arm-brings-custom-instruct...
But things will become really interesting at the point ARM would be eaten by Nvidia. I've prepared a big pile of popcorn just in case.
Agreed on the popcorn though!!