> There's reason RV32E and RV64E, with half the registers, are a thing. RV32I/RV64I isn't small enough.

This is actually kind of counter to your point. The really tiny micro-controllers from the 80s only had 224 bits of registers. RV32E is at least twice that (16 registers*32 bits), and modern mcus generally use 2-4kbs of sram, so the overhead of a 32 bit barrel shifter is pretty minimal.