> RISC-V doesn’t even support running 32-bit code on 64-bit processors without a recompile. In a sense, 32-bit RISC-V is a vaguely similar but incompatible ISA to 64-bit RISC-V

RV32 and RV64 are considered distinct ISAs. But designed to divert as little as practical.

Apart from the register size, differences are small enough to be (almost!) irrelevant. If you know RV32I assembly, then you know RV64I assembly & vice versa. Moving code between those is at worst a re-assemble away. Also it should be easy to support execution of RV32 binaries in userspace on a RV64 cpu (if some implementations supporting that don't exist already).

AIUI, profiles were meant to provide a common target for eg. Linux distributions. Cases where you want 1 "generic" binary to support a variety of hardware like phone/tablet/SBC/desktop. Since these target the common case, yes profiles can be expected to grow & accumulate legacy cruft over time just like other ISAs. But for embedded or high-performance computing (HPC), this doesn't matter as code will be compiled for the specific hardware anyway. RISC-V's modular ISA is a great asset there.

In the meanwhile: loootts of legacy cruft dumped (esp. compared to the insane x86 world). That's always welcome. Nothing's fixed in stone (not even silicon, imho), and tech should learn from past mistakes, improve things & move forward.