I think that would be very useful. Since its already possible to check history its just an enhancement to the game.

I would use this to mark territories where I know an enemy started.

+1 to the opening post. :)

Obviously this should be low priority, as it is just another, more convenient way to do something you can already do. However, if Fizzer has extra time (hah) then I think it would definitely be a thing worth working on (or at least allow you to pm yourself/save notes on a game.

It is nice that we can add any note to any territory. Not just for wasteland, it could be used for many other things, like marking down estimated number of units, strategy notes etc.

I'd like to be able to make notes, keep track of where you've seen people, etc. Not placed automatically, of course, but by your own reckoning. If you want to make a note, sure. You may be wrong, but it'd be a potentially helpful tool, if you're running a lot of games. Also could be interesting on team games, if they could be shared. Not sure about how easily implemented it would be on anything real time(and that's really the only sort of games I play, so not a huge concern for me), but multi-day seem like they may benefit from noting that you last saw X enemies at Y location on turn Z.

Those hidden wastelands in for example turn 7 could already been attack by other players, those numbers you draw could be wrong. So don't be a fool and use reconnaissance card.
This idea is the same as draw a picture on the back of memory cards to remind where the equal parts are located.
I wouldn't recommend to join any game with wastelands AND dense or complete fog