This is a really interesting idea for 3D modeling in general...

You know how when you use Abelton Live and you split a track meaning cutting part of the audio off and deleting it then later if you go back to the track you could grab one of the edges then pull it out again and extend the track where it's the same as it was never split.. IE the split of the track earlier was nondestructive so all the data is still inside there. What if you could do that with 3D modeling like a mesh like you delete a bunch of faces and then you could just go back later and if you wanna take it back you could just extend them out again from where are you deleted them from before....it would totally pimp the undo process