Indeed, you need the whole stack. However, the (non-temporal) memory safety alone is still quite easy to get - the compiler will take care of it, as a programmer you just need to make sure your code doesn't get in the way by eg manually stashing pointers into non-pointer types. It's been demonstrated on large, real-world code bases, such as FreeBSD and PostgreSQL.

(Disclaimer: been there, done that, part of the CHERI team)