Content wise probably three tracks per planet will work.
Though I would like to see a lot more work put into existing tracks once the roster is bolstered. So get the three or four remaining maps in the game in a functional sense, let the community test them and provide feedback and then go back to the earlier stages and give them a final lick of polish.
For me FIC and Alhatra (reverse) are the only tracks that are 95% complete.
Yuri – I think there are flow issues there and an overabundance of narrow sections.
Wastes – It looks so much better in reverse (perhaps this can become the default) but I like the layout of this track.
Transport – One of my least favourite tracks – relatively boring layout – visually uninteresting – to many insta stop barriers.
Islands – tons of flow issues – very ambitious though and I hope it comes together.
Speed Bowl – near complete for what it is – a bit visually uninteresting – jumps and things scattered on the track appear tacked on.
Sky track – layout is solid – visually uninteresting though – tonally this track is off, it feels more like a scramble level then a track proper. Needs to be more grounded on Orbital Prime. Perhaps ad assets used in Haze once complete.
Haze – great track with visual flair promised so no complaints here!
Acrophobia – I like this track – it may be a bit freaking hard but I’ll let the community correct me there. Has enough to make it feel grounded and is far less barren then Skytrack. Again, some of the jump/direction indicators appear tacked on or place holder.
1 battle map per planet would be great too.
I think, with the Eversor and final Terra vehicle, the roster of cars will be full enough – new teams can be released when Caged is able.
Game Modes are pretty full as is – If all the above is up to scratch i.e. great tracks and cars, multiplayer will be enough to keep the community happy. A league mode in whatever structure makes sense would be fine for single player.
For me that would make GRIP excellent and the devs can build from there in whatever direction makes the most sense financially and for the community. Anything else is gravy