Honestly, it sounds good. Probably more to the point, if I have someone sitting idle in the group for any length of time, they'll get recalled. If I'm constantly tagging the same people idle... I just won't let them join.
I think allowing them to set their own (and remove if set) flags is a good idea. Recalling is the honest thing to do, yes, but can potentially mess up the protect chain, the occasional person doesn't have gate to get back, or if you're in a nogate area, etc. As a leader, I think it'd be pretty cool for someone to say "Damn, I gotta take care of something quick, brb" set themselves idle, and then flag themselves back 5-10 minutes later. They didn't gain anything while afk, took care of their stuff, and generally did the most honorable thing with a minimum of hastle. I don't see that needing a punishment. At least not as long as I have the option of flagging them over their flag if I think they're abusing the system.
And honestly, if the system doesn't work, I'm sure you'll hear plenty of suggestions and complaints on the crier
