in case of search, wouldn't law enforcement agency seize ALL your equipment, not just the one box you point them to saying:
"here's my diskless tor relay. take it!" ?
So? The idea is not to protect your browsing habits. It's to protect the users of your node. They won't leave a (permanent) trace. Of course if they go for your devices they can look at your disks and see what _you_ were doing. Different thing though.
The important thing is storing the ssl key in a secure manner.