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I don't think it's right to automatically concede a game just on principle, especially after playing for, say, 4 hours. I consider it disrespectful to myself as an opponent (except in cases where the situation is truly bad and it's practically impossible to play, or if there are real-life issues). Because time is precious, and spending it without getting a satisfactory result, only to receive a message like "I conceded, thanks for the game," is, at the very least, foolish. Those who want a "+..." in their rating will be happy with it, but not everyone plays for that.
And, I think adding a rule about automatic concessions is a bad idea, no matter how you look at it.