This is exactly the type of thing the timebank is for: all that is needed is a minimum timebank setting in your challenge settings. Russ has said he'll look into the challenge filters next time he's working on the RHP code, so fingers crossed...
The proposal above is basically a second tire timebank, over and above the present one. A level of complexity too far methinks. And it would not be applicable in tournaments and so on, so wouldn't help out in the recent flaming anyway.
The current thread of skeeter/seadevil is very similar to the Edmond Dantes dispute some time ago, where a player is publically alleged to play as slowly as possible with the aim of winning when their opponent finally does go on a true vacation. While such behavior would obviously be annoying if actually the case, the good use of timebank settings (i.e. always big enough for a holiday) should remove the majority of instances it could be applied.
But any system devised will be open to abuse of one sort or another: whether strategic slow play or vacation flag abuse or whatever. Keep in mind that its only a game: play it, move on. If you don't like somebody's style, don't play them again.