Hey! I tried your prototype, and while it seems like it's in its VERY early stages, I'll try to give some comments on what it feels like and where I could see it heading.
From the control methods, I think what I could see working is the individual motors control - it is simple enough to understand and it instantly provides a bit of depth to the handling of the rockets.
In that regard, it also provides funny scenarios while you're learning how to control the rockets, almost QWOP style - this could favor leaning towards the more "friendslop"/intentionally frustrating angle of making races where everyone is bad and keeps crashing into each other at first. Not sure if this is what you have in mind, but that's where my head went.
On the more formal side, the map vs ship ratio seems correct to not be exceedingly hard. A small tweak I would make is have some degree of directional auto-correct after crashing into a wall, since you tend to spin around several times and it's very hard to recover the proper direction without thrashing all around (the turn radius tends to be a bit high).
I could not test the multiplayer, so I'm basing my impressions off of just taking the ships for a few spins.
Overall, right now it seems like a proof of concept more than anything, and there could be something there - but right now as it stands, it could be a million different things, so I'd decide on that moving forward.