September Update
Posted one month ago
The Undo system isn't perfect, but it got a bit better this month.

Previously, for undo, we were generally keeping a copy of the scene after ever change, and loading that when you undid. This is the lazy way to do it.. and lots of people noticed that it was getting quite slow in larger scenes.

The new system saves individual GameObjects and Components, so it's a lot faster. It can go beyond that though, and you can provide a undo/redo actions, to be the most optimal it can be.