My thought are that less but very polished content early is the way to go (like overwatch, arms, splatoon...) followed by strong support through the tail end of the games life cycle and before the inevitable (and hopeful) focus on a fully fledged sequel - GRIP STAGE 2!!!
For the initial push - to get GRIP ready for a digital release on PC and PS4 my feeling is that;
- the 4 planets in the game cover the initial launch.
- I would hope to see 4 tracks per planet.
- 4 racing teams
- basic league mode (like RC1)
- x Scramble maps
- only the current battle maps will do
For me (if fully polished and perfect) this would make a digital copy of GRIP fantastic value.
Following this, the release of a fifth planet can form the first DLC;
- 3-4 new tracks on this planet
- and the remaining battle maps can make an appearance (possibly 1 battle map per planet) - this may not need to be expanded if the popularity of the mode isn't there.
For the second DLC;
- a few new tracks (filling in the gaps and fleshing out the content) and,
- a new race team.
For the third DLC;
- Single player campaign/story mode
- a new racing team
- and the inclusion of any community (and dev teams) final demands

Following this can be a game of the year or disk release of the game.
So these are my thoughts - what are yours? ...When will there be enough content in the game and when can Chris and the team switch gears to polish mode... Damn I needs to see me some polish!!