We discussed this. It's very problematic when players are performing actions simultaneously, especially when some of those actions often have effects on others. Here are some of the ideas we tossed around:

A: Add a "Return to start of Local phase" button, available only when new cards haven't been revealed.
+ Fairly straightforward
- Other players can undo your actions
- Any sort of R+D disables this

B: Add a "Undo actions since other players' most recent action or since you last drew cards" button
+ Fairly reliable in a turn-based game
- Fairly useless in a real-time game
- Even just the description of that button can tell you that it's going to be frustrating to use

C: Add a smart "Undo all of my actions" button that doesn't undo anything affecting other players
+ This would be pretty nice
- This would be really hard

D: Add an "Undo most recent action" button, with no option to undo further than that
+ Relatively simple, probably meets most players' needs
+ Probably unnecessary to consider what other players have done since; we can disable the button if the most recent action gave a card to another player or revealed new cards
- Players will definitely ask for more
- Rolling back just part of the game state is still very difficult even for atomic actions

To add to this, even the "simple" solutions are difficult to implement in a reliable manner. We've taken efforts to allow undoing where possible (you can un-pass your turn in the local phase and change your vote on the global project). We've also seen the request for more confirmation buttons, which will further reduce blayer error.

Undo is a feature we wanted from the beginning, but the game's format makes it less feasible to implement for the reasons Mogri described. If you'd like to discuss some options, let's email directly and brainstorm together.

We'll investigate adding a player-based undo for actions that don't affect other players. The implementation is tricky even for limited circumstances, so it may take a little while to roll it out.

We have added an option for undo. It works on a per-player basis, so you can undo your own moves even if other players have taken many moves since then.

By the nature of the game, many actions will prevent you from undoing your action. These include tucking a card under a global or crisis card (because other players' action may gain bonuses after that point), changes that affect the board such as adding cubes to the thermometer, transferring cards or communities in crisis to/from other players, and many more actions. Basically, actions that have an effect on other players' actions cannot be undone.

As you play around with the new undo system, hopefully you can help us decide whether it's an improvement or whether it creates confusion. While we're certain that a more expansive version of undo will always be requested, we've already made efforts to allow it in every feasible situation (it even undiscards cards that you have spent if they're still in the discard pile). Consequently, we've reached the limit of the undo option and we're now evaluating whether the new system will be beneficial for players in its current state.