I'd like to be able to set it to where players become visible if any of the following occurs:

-Struck by player (damage-in by player)
-Fall into lava (environmental damage)
-Use switch/door (interact with environment)

I'd like to give Vanish to more players on my server (than just Admins), but with the principle that it would be for more of a realism->RPG thing, where invisible players are treated like "rogues/assassins" or "Scouts" in Team Fortress 2.

This feature could be used in conjunction with the existing ability to make players targetable by mobs, so they have to carefully avoid mobs to avoid being revealed.

In addition to this, I would really like to see an addition to the 'No Chat' functionality, where, the player 'is' capable of chatting, but doing so would result in the vanished player appearing.

A few things to note:

A player that can't see an invisible player, can never cause them damage with swords or punching.

This request feels more like a separate plugin request, incorporating VNP, than a VNP feature request. It will be more likely possible once VNP 4.0 comes out.