Glad to hear you might be up for the idea, and yeah I hadn't thought about the balance side of things, although to be honest I cant imagine taking it too competitively, 90% of the satisfaction is the physics, for me anyway!
If your intending to add to the game I would be interested to see some more complexities to gameplay, for instance, game modes like capture the marble? Or if your domino trail length was not capped, and maybe with a bigger table you could set traps with your trail. Maybe if you could switch to control any of your placed dominoes this could make it more tactical too? If you could jump you might even be able to make towers, although the practicality of this I'm not sure.
Anyways, just ideas