MikeFerrara once bubbled...
Should a card really lapse?
Well you could do it like membership - getting that annual sticker on your card.
Although I've never been on a boat in California that ignores cert cards, I've heard plenty of posts here about how many resorts and boats around the world don't care. So for those boats that just want to see a card - pull it out - who cares when you got it. But for special rank and priviledge devise a system that requires testing or recert.
The "sticker" would get you special benefits, membership, etc and could come from having a review of your skills done through some mechanism. For example a phone interview with a course director or IDC staff instructor - where they give you random questions and you have to answer them. Or some type of on-line testing with a timer so you can't spend days looking up the answers, then submit the test.
Really though it's a logistical nightmare having some sort of PADI appointed auditor who calls with a weeks notice. They would shadow you on a class, or if none were scheduled, supervise a test or verbal exam. Or regional offices could be setup to hosts review weekends, where instructors flock to get pointers and tips and take a test and then get a sticker or piece of "authentic paper" indicating attendance. Then there's the issue of requiring attendance, and the frequency and availability of LOCAL opportunities. Perhaps the Internet using netmeeting, or MSN Messenger video, or AOL IM with some sort of unique identity authentication mechanism (not yet developed). Using this tool you could conference and participate in to a regional, take on-line tests even submit questions and have interactive sessions. But this would require PC ownership and not everyone in the world even has that. But let's face it every instructor got to an IDC and an IE at some point, so if it was absolutely required they could do it again. But it all comes down to money.
What am I saying none of this would ever work ... it's all about money how would you fund it. Instructors already pay out a fortune each year in liability insurance, personal insurance, gear replacement, membership dues, then add recertification fees - they'd hop right over to an organization that doesn't require it. Only the universal standards board could inact a change of his magnitude and it would be slow to adopt.
I've re-thought my position no re-certification.