You know, Kai, actually I was thinking if we can rely on joml... it'd be cool, what do you think?
I don't know what requirements a physics engine like bullet has regarding math.
I'd suggest you take one or two weeks digging inside bullet's sources, playing with a native bullet build for a while to get a feeling, and then see if JOML can help you with anything.
You see, JOML is geared towards transformation calculations for OpenGL rendering. Not towards a physics library.
So I reckon you have to write most algorithms and data structures by hand anyways. Of course, there are basic data structures you always need, like vec3 for acceleration, velocity and position vectors. But that's basically it, I guess.
Also understand that JOML tries to cover far less surface (meaning set of requirements) than what a full-blown physics engine like bullet does.
And a physics engine is driven by alot more forces (all kinds of features (rigid body, soft body, ...), performance, runtime-footprint, ) to be useful to a broad set of people than what a simple linear algebra library like JOML is.