The ParticleSystemForceField component, if allowed on avatars could open up possibilities for inter-avatar interactions not provided for fully by Udon.
This is a new canny just for avatars, because as of the latest 2018 Open Beta, VRChat has made great strides and world authors have more than we could have imagined when the [original canny] (https://vrchat.canny.io/open-beta/p/whitelist-particlesystemforcefield-component-for-avatarworld-interaction) was written! Udon has access to bone transforms, and ParticleSystemForceField was whitelisted in SDK3 worlds!
Mimi made an example showing what this component can do: https://i.imgur.com/yglb74H.gifv
Tupper has made a statement saying that "We have no plans to add this component to the avatar whitelist." However, I think the ability to use ParticleSystemForceField on **avatars** still deserves a canny.
One of the magical things about VRChat is you can create new and amazing avatars and share them with your friends in public worlds, without having to interrupt social gatherings and invite friends to your own world. For this reason, the desire exists for more than just udon and world whitelists.
A component such as this one can be easily disabled by world creators by simply removing Player, MirrorReflection and PlayerLocal from a particle system's "Influence mask". For this reason, it still seems like a perfect candidate for avatars.
If performance is a concern, it could put the avatar directly into Very Poor status and be part of the Particle Systems safety and performance category.