It is not problem to make particles independent. Most of them (emitter, fire, snow, explosion, spiral) use Sprite2D as particle object which can be extended to support independence.
The big problem is to get effect what we want. A particle at the moment of creation must get its start speed from base object + emitting speed. But at the moment we cannot know from base object its speed. At least there no good API-way to make this. Of course we can compare previous pos & current pos and divide delta by elapsed time, but that's very rough approach.
Note that all the particle systems that depend on Sprite2D are deprecated and will be removed at some point. They are too slow.
If we need particle independence it is better implemented in the new and fast 'particles' mesh.