"see i could just have it do special work with only the STA and LDA commands, and whenever any other command affects those registers the values would fall through or do unpredictable things on read-only registers, and i think thats what should happen, right? then i would only be ignoring writes to the registers using any other opcode then STA"
A lot of programs would fail to work in such a situation. At least my programs would fail. My engines tend to do a lot of LDX, LDY, BIT, STX, and STY on the I/O registers so that I don't have to use as many local variables on zero page. Some programs even do R/M/W instructions (INC, DEC, ASL, LSR, ROL, ROR) on I/O registers in their copy protection attestation code.