It's a tough question, and one I've thought about a lot. I think, on balance, my answer is 'yes', because they are still part of the community - they may not be posting much these days (I include myself in that), but they have posted a lot in the past, and are what has helped make the board great over the course of a generation. I think it's unreasonable to disenfranchise these people. Also, where's your cutoff - if I post once a month in different threads, and DB posts twice a year but takes part in a 'conversation' then who has contributed more? I don't think it's possible to judge these things.
As for Imposter's point...it's theoretically sound, but, havingg been a mod on here before, I'm also aware of how much time it takes up. His method would take ages to sort out. I feel that one thread on here, on the first day back after the trial, is the answer. To ensure it stays at the top of the board, you could also have it be the only thread on here for a day, and then reopen the board after its conclusion.
I think people have the right to decide not to move if they don't want to.