If there's interest, I can definitely take a crack at it!

My current plan was to introduce some new particle types as there is some pretty stimulating emergent behavior that comes out particles with different rules interacting with one another.

I'm also really interested in exploring 2D velocity and acceleration- how we could go about enabling particles to be thrown and bounce off of walls- or each other.

If you don't mind spoiling your plans, are you thinking of continuing with the subclass-per-particle type approach, or eventually moving to something like a simple ECS architecture?

A full ECS architecture? I don't plan on it. But using some sort of trait / component structure could be worth if enough particles with a mixture of different and overlapping behaviors were introduced.