The ParticleSystemForceField component new to Unity 2018, combined with "external forces" module can open up a whole new breadth of avatar/world interactions not seen since Ik controlled GPU Particles.

Mimi made an example showing what this component can do:

For the module to be useful, it must be allowed on avatars so that (combined with IKFollower) leg and arm positions can emit forces. Doing so can enable new types of 30dof interactions not seen before between avatars or between avatars and particle systems in worlds.

Worlds that wish to block avatar particle interactions must only uncheck avatar layers including Player, MirrorReflection etc. For this reason it should be safe to allow avatars to carry this component without impeding world creation.