When originally invented the x86 instruction set was efficient - the most-used instructions had shorter byte code sequences. But eventually some instructions got 'left behind' by the compilers. There are a whole host of single-byte instructions that are never, ever used by a compiler - the register exchange instructions for instance (xchg eax, ebx). Compilers just schedule destination registers carefully, never need to swap them around.

Also the whole set of exchange-register-with-itself were defined but never used. E.g. xchg ax,ax which does nothing in one byte. In fact that one was considered useful, its used as the 'no-op' instruction (0x90) right? But what about xchg bx,bx, xchg cx,cx and so on? Just wasted single-byte opcodes. Leaving actual common instructions to use longer bytecode sequences.

So maybe an executable should begin with an opcode-decode-table that is loaded with the code, that tells the hardware what byte sequences mean what instructions. So each executable code can be essentially compressed, using optimum coding for exactly the instructions that code uses most often. Just thinking out loud.