Klein Bottles only have one surface so they are the easiest thing to clean
I'll play devil's advocate - the physics engine can't do triangles! Well it can't do primitive triangles which would be the logical thing you'd think. Infact it can't do much else beyond what it's already doing.
In the way of primitives it can do spheres, boxes, capped cylinders, regular flat-ended cylinders & infinite planes that can't have their position adjusted... Which is a list of what we already have.
Other than that you have to go down the full polygon model route, so no real point in asking for a triangle. Be greedy, place demands for a stack of shapes instead. Demand model support in mods while you're at it.
Hampa's gonna hate me for provoking this
What engine is he using that cant support triangles? Possible one for the most basic shapes....
BY asking for that, hampa would have to redesign the engine or get a new one. Making it possibly for other stuff to happen as well.