True, but that still gave you access to only a subset of the 80386 instructions. For the others, you had to write them entirely in unreadable hexadecimal, addi

True, but that still gave you access to only a subset of the 80386 instructions. For the others, you had to write them entirely in unreadable hexadecimal, adding a data-size prefix was not enough. By far the most useful were the 32-bit addressing modes. With your method, you could access those by adding just a "db $67" prefix, but then the addressing modes would have been greatly obfuscated by the 80286 notation, so that would not have been much better than writing the entire instruction in hexadecimal.