I like this idea as well.
They should also have a setting where you can automatically accept challenges within your range of play where the range includes increments.
Honestly I really can't stand playing without a fischer increment. When I see people on the top board just trying to run the clock out with random moves its pretty sad. In general chess.com should have more general settings with a decent increment.
Since tablet users (and I assume other portable devices) can't hover their mouse over a dot on the seek graph to reveal the time control being solicited by a seek, I suggest that a color change (perhaps blue instead of green) should be assigned to those seeks which have a secondary time increment.