Iirc the specific reason behind this is
- sudo by default requires a tty to run
- vim's bang spawns a tty to execute commands
- nvim's bang executes the command directly, then pipes the output to nvim
As a result, sudo (without args) can't work in nvim as it doesn't have a tty to prompt the user for passwords. Nvim also used to do what vim did, but they found out spawning the tty was causing other issues (still present in vim) so they changed it.
How good are the RISC-V vector instructions implementations IRL? I've never heard of them. My experience with ARM is that even on certain data center chips the performance gains are abyssal (when using highly optimized libraries such as dpdk)