Eduardo,
The project looks amazing, congratulations!
I know you're not interested to add 'modern' features such as HDMI, but what about a 15 Khz RGB out?
Concerning games, I'd love to see the following titles on the Prometheus library (in alphabetical order):
1942 & 1943, Bomb Jack, Commando, Elevator Action, Enduro Racer, Escape from the Planet of the Robot Monsters (feasible?), Exerion, Galaga, Ghosts'N Goblins, Jungle King, Moon Cresta, Moon Patrol, Pleiads, Q*bert, Scramble, Shadow Warriors (feasible?), Terra Cresta, Xevious and Zaxxon.