As discussed in the IRC Channel I note down what ideas I have concerning the implementation of the inversion:

Way wanted the inversion to be not containable thus a few mechanics should be added:

~Preventing the player to encase the inverted area:
If the will in the aura rises above a certain threshold it can sometimes cause a "tear" in the fabric of reality to appear.
[Trigger] If the check to erode or invert blocks fails x times because the block is already inverted or is not able to be inverted this event can trigger
Method: spawn a entity with no gravity on random coordinates which emits a sound warning the player. After a few moments the tear creates an implosion / black hole that suck up blocks in radius 1-5 of he entity.
Why not explosions? Because the player might have blast resistant blocks from other mods or obsidian.

~preventing the player to make it too easy in void worlds:
If the aura rises above a certain threshold it can bring material from the demon realm.
[Trigger] If the check to invert / erode blocks fail x times in a row because the block is air
Method: spawn an orb or hemisphere with radius 2-7 at random coordinates. Made out of inverted dirt and or stone.
Why not single blocks?
Void world would be very hard to traverse and having many floating islands and orbs might look nice. While giving ample space for mobs to spawn.

feel free to add or comment

Missing suggestion label.