That's not realistic. Too much stuff is board-dependent and trusting vendors to upstream it (or even disclose documentation) isn't going to work never ever. I think what should be done instead is to swap privilege levels so that after-boot firmware services runs under operating systems, not above it. ACPI, with all it's sins, is pretty close. On the other hand, RISC-V made same old mistake of introducing SMM under other name into their supervisor spec and addeed their own secret sauce of forcing damn TIMER interface to go via SBI (seriously, WHY? High timer latency was known to be a problem om x86s requiring all sorts of weird tricks since Win95 or so).