After many years, the Unity editor was apparently ported to Linux.  We'll see if it's another 1 & done like Main Actor, Microsoft Word, Internet Explorer, & Skype were.  It requires a unity account of course & an internet connection for license management.  After discovering how much would have to be programmed from scratch in Godot, the lion kingdom started viewing Unity tutorials.  It has a whole lot more examples than Godot. Unity theoretically has race track frameworks you can drop models in.  It has an automated road builder which can generate 3D paths.

The licensing & ownership of the game engine is less of a factor over time.  The mane showstopper is no-one has really shown a physics system that comes close to Asphalt 9.

Cheap physics

The lion kingdom has considered different options for solving the physics problem.  The stock godot physics system is crap.  Getting useful results from godot would either take too long or require far more engineering than is worth it.  If it was easy, everyone would be modeling the Asphalt 9 physics.

What has risen in showers is just modeling physics the way it was done on 8 bit side scrollers.  They didn't have any physics.  The complete flight path down the track would be hard coded.  There would be static acceleration & rotation in the direction of the flight path.  The user could turn the rocket with left & right input to add offset to the preprogrammed path, but it would always have a static tendency to accelerate & rotate in the preprogrammed direction.  

Speed would use simple acceleration equations & limits.  If the user hits nitro, it accelerates to a certain limit.  Liftoff accelerates to a certain limit.  Hitting a ramp would be a boolean operation rather than a physical simulation of a ramp.  When the player hits the end of the preprogrammed flight path, the game is over.

The game still absolutely would require collision detection.  Godot's collision detection is just a boolean operation.  It can't give the direction of the collision or where in the model the collision happened.  All it knows is if the player hit the side of the track, a player hit another player, or a player hit a ramp.  Collision reactions would have to be about as limited as they were in 8 bit side scrollers.  We can get the vector between 2 players & which side of the track, at least.

If it hits the side of the track, it needs to reverse the velocity perpendicular to the track & constrain the rotation to straight down the track, but the sides aren't parallel to the path.  If it hits another player, it knows the velocity vectors of the 2 players so it can use a simple elastic collision between 2 masses.  The rotation wouldn't change.  The shape of the players would be ignored.  RUD's would have the fragments keep going in the player's last velocity vector while expanding, but bounce off of track walls according to simple collision rules.  It would have a very 80's appearance.

A big problem with rocket simulators is how slow they are compared to car racers.  Elon mentioned in an interview that the starship is going to take off much faster than a normal rocket, so the start could actually be modeled more like a car race while being accurate.