I would be ecstatic to have an undo button. I've been playing this game for over 6 years and the second most common thing I wish there was, is an undo button but is only available 1x per game for example, so that it's still fair.
It would be nice to get to text teammates and ask for help or pointers on the game. You could be able to make friends around the world, but you would also need a way to block a person if they were not being respectful
If you get really stuck on a level you should be able to get some help. Maybe you could add a help button after 10-15 losses that would give you a hint on how you can defeat the level your stuck on.