Looks really good. "Robotron 2084" is an Arcade-classic, looking forward to this conversion of the game here for the C64.
By the way, on the Amiga a very similar game named "Llamatron 2112" exists and the way, they solved it with the controls for 1-button-joysticks there in this game, is really superb. Works really very good, as a player you even don't miss dual-joysticks then. Maybe you could have a look at this Amiga game one time and when you like these controls, it could be solved in a similar way, here in "Robotron 2064"?
Only a suggestion of course, but i wanted to have this mentioned, because in my eyes, Llamatron plays really great, even with only one 1-button-controller.