My suggestion is to add an option to make the player take a configurable amount of damage when teleporting out of the void. This would be useful for the infinite fall mode. If the player falls under a floating island, they would land back on top of it. However, if they fall while under nothing, they would take damage then die rather than infinitely fall.

Hey! This is already supported by VoidSpawn. This can be done via /vs option set damage <amount>.