Need to decide 

• whether to further simplify 

or go the other way and ...

• add further general purpose registers 
• and IO - IO might be achieved by memory mapping the devices, or by adding further special purpose registers etc

Also ...

• consider adopting a higher level language - ? something like ttlcpu ? 
• deciding whether to use higher level instructions to drive the microcode or just put this complexity in the Assembler (or Compiler) instead

And ..

• working out how to integrate with VGA - probably using a NovaVGA and some shift registers as IO.
•  working out how to integrate with input devices (eg a potentiometer if we were to implement a Pong game for instance)