Well one thing that can be added is accessibility, again. In other words, adjusting the colours and enabling keybourd-only input.
Another improvement is to change the art-work. As was said earlier another background that can be used is an eight spoked wheel, with or without the rim. A bitmap can be used for the background too. Use your imagination, is the playing field scratched on stone? scribbled into sand? or in-laid in wood? 3-D sprites can also be used for the playing pieces.
Other improvements range from optimizing the program to adding more moves to the 'AI's' look-ahead.