You can’t (not cumulative). A way to enforce (and fairness) can be to switch to the opponent as the new AI’s target after each occurence.
Besides the AI don’t mention if it’s a good or bad move. (Graph is not visible )
A variant could be to switch when the winning color changes (not telling who is winning)
Oh, I thought you meant mistakes are not accumulated (i.e. three one point mistakes are not equal to one three point mistake).
Maybe switch after each move by white if the winning color changed since the last switch?
If we switch colors each time the balance of winning chances switches, then the loser will stay loser and winner winner.
So what counts is if you can reverse more times as your opponent, as the final result.
It’s still not simple as only one player can reverse. (Loser staying loser after each reverse)This will need two games, with a different leading player in the first moves. So we can compare the “getting a reverse performance”.
Another way to avoid to play two games would to let the reversing happening only half of times. But in many games, there are not that many times that the lead switch.
For example
Player A color O takes the lead
After one of his moves he has + 5ptz(as an example, Arbitrary value ) and that triggers reverse
B play his color X and then play again O
(Or
B after his move -5pts triggers reverse
He plays again, O this time.)
Game continues, A playing X(leading) and B O
At some point the winning change,
A keep playing X (losing) and B O
One more reverse situation happen X (winning)
Exchange of colors happens
A plays now O (losing) and B X
Conclusion
Each player played each color .one time losing, one time winning with each of them.
Even with less sophistication, if we could have a program which switch colors for passing over a win% or for a switch between white and black leading, we could imagine teaching games too where every time the stronger has a too big lead, he get a new challenge to reverse the game, or the weaker playing well got the chance to take white…
And could be a nice training between same level players to share ideas around a game with a little bit of AI input.
Forbid an opponent from challenging you in a ladder if they are already on turn in one of the countless correspondence games they have started with you.
Or maybe just a warning pop-up.
“You already have N games with this player and you’re not making moves in those games. Are you sure you want to start a new one?”
Did someone already mention “swap colour go”?
Something like:
A: Ok, I think I’ve lost this game
B: What? I would feel comfortable with your colour now.
A: Ok, let’s swap colour and continue the game
Oh, yes, someone did and I already liked it! 
More game options:
Pause game at night time
Night time start time
Night time end time
An AI to help us using OGS and its forum, answering some repetitive questions.
Considering how badly the forum organization makes information accessible, and how the main site is like at times (too lazy to go search that meme btw)
A doubling-cube feature.
Before your turn, you can offer to double the stakes.
A player cannot double twice in a row: when A plays against B, if the game has already been doubled at least once and A was the last player to offer to double, then only B can offer to double.
I believe standard practice is that player B has a 3rd choice which is to redouble.
Hehe.
Under good play, to maximize the value/EV of doubling, if you are ahead, you generally want to offer a double no later than when you think your practical chances are ~80% or higher to win, since that’s the point where your opponent will want to resign rather than accept a game that is both doubled and highly unfavorable for them (if they do accept past that point, it’s even better on average for you than them resigning even if some percent of doubled games you end up losing).
You don’t want to wait any longer than that to double, because if the opponent is behaving sensibly then there’s no upside to waiting. Wait longer to gain even more of an advantage before doubling and they’ll still only just resign in response, so you might as well double and have them resign now. And there is downside to waiting, since you could blunder in the meantime.
So anyways, the result would be that players would be incentivized to use the double not merely as a way to cut short a won game, but actually well before that, when they feel they are ahead but when the game is still not certain. It might be interesting to see for players of each different level where that point is, where they would subjectively estimate their own practical chances to be 75-80%.
An AI that estimates the level of new players. The rating of the player will be determined
Edit: Animiral had more or less the same idea here.
And within 5 minutes of each other 
Permutable branches in conditional moves: during endgme, it is quite frequent that several parts of the board don’t interact, so that sequences ABCD… and A’B’C’D’… can be permuted. So we should be able to select 2 or more branches starting from the same vertex and declare them permutable.
Unconditional moves:
If a is ever played, respond with b regardless of the board state 
You’re going to regret this one when A is a ladder breaker or a ko threat!
Collection of cute animals videos. If you win a game, you can watch 1 video.
(If you lose, you are not allowed until you win)
A “get your game reviewed” kind of raffle.
You submit a game in the pool and one is randomly chosen to be featured in a banner. Might get more people, of all ranks, to participate in reviews.
