I would ditch the SD cards entirely and boot off of USB attached SATA SSDs. But your idea still sounds cool if you can't or don't want to invest in SSDs!
I've enjoyed btrfs on my laptops, definitely seems stable, and using BEES foe dedupe is rad (maybe don't do that on an sd card tho...)
Cool they built this in Second Life, now do it for real in the real world!
/s
Good cars, good batteries, seems like a no-brainer.