> Only difference being that you need to do a bit more work to determine negativeness (work which in hardware you'd already likely have the bulk of for determining is-zero).

The work needed to calculate the overflow flag (done in every add/sub operation in most ISAs) is also way more complicated when the high bit does not represent sign.

Oh, true. Even further down low-level/frequently-unused details though; and RISC-V does without it (/ flags in general) roughly fine.