Just do a rollover every cycle ...

Once you've had your elections, every FAS/SIG applies to be renewed - it should be a very simple tick-box procedure. As people contribute they get added to the new FAS/SIG, a tick-box exercise if they were already a contributor from the previous FAS/SIG, or normal procedures if not.

Then when the next election comes round, only people in the new FAS/SIG can vote ...

So as long as people keep contributing, nothing changes. If they don't contribute for one entire Fedora cycle, they fall off - how long is a cycle?

And if any FAS/SIG goes inactive, that falls off too.

Cheers,
Wol