I think it has already been stated that undoes to decisions from which no new information has been gained will at some point be automatic,
I certainly recall having read that too. No doubt implementing it in the general case would be quite time-consuming because of the need to evaluate correctly whether new information has been gained. There are, however, some simple cases where it could be implemented very quickly and probably should be, simply because it's an undo of something that the opponent doesn't even know has happened. Consider the following scenario that happened to me yesterday:
- I played an Action that drew a card and gave me an action point.
- I clicked on 'End Actions'.
- I realised that I'd meant to play another Action card first.
- I clicked on 'Undo'.
- The undo request was denied.
A first I was surprised that my opponent had denied the undo request, but I almost immediately realised that to him it seemed that I was trying to undo the play of the Action that drew a card: there would have been nothing in his log to indicate that I had chosen to end my Action phase and that it was that that I was wanting to undo.
I could, I suppose, have tried explaining the nature of the undo request via chat, but I had no idea whether my opponent spoke English, so I just accepted the consequences of my carelessness and got on with the game.