x86 and ARM will both face fierce pressure from Risc-V. It will start dominating at the low end and displace existing architectures like Atmel, PIC and even the very old 8051. That's because both the low end CPU design and tool chain are free. The Raspberry Pi RP2040 has extra Risc-V cores because why not? They aren't being used right now, but they will be accessible at some point. Very simple Risc-V chips can be had for $0.10 (US) right now in small quantities.
At higher end performance there are lots of players who can enter the marketplace because of the open nature of Risc-V. Some of them are IP vendors who would like to sell specific capabilities like super-scalar and vector extensions. For high performance/throughput it could be advantageous to integrate interconnect silicon right on the CPU chip. Risc-V will eventually come to the supercomputer space.
And don't forget about China, who has strong economic and political reasons to be free from foreign control of such critical technology. Even if they can't keep up with TMSC they have a vast domestic market and could compete in the international market by being cost effective, even if they aren't the fastest.
Weirdly enough Microsoft is in a similar position. They might like to have the option of competing with the Apple M CPU series with a chip of their own.