Registering is one of the problems, but without taking them apart and cleaning them other problems could arise. The contact leaflets becoming deformed from sticking or springs rusting if cleaned improperly would probably be the biggest problem, but others have noted changes in spring-rate and/or the <click> from blue switches from not being completely cleaned after hours of soaking.
Thanks for the replies
Hmm, remember seeing ripster leave out some switches for quite a while outside and they did not rust. Can't seem to find a guide on how to take apart mx switches.
I USED to have lots of Guides for repairing switches at Geekhack but iMav deleted them!
Ask HIM where they are.
I'll be posting backups sometime at /reddit/mechanicalkeyboards/.