Just read the 40-odd posts in New Members Discussion topic. The following two things came to mind:
Normally, on e+ (and in most other cups and tournaments), hasn't the rule been:
"Any player who joined to another clan has to wait X matches before he can play (X being between 1 and 4), UNLESS he was already part of another participating clan's roster (even if clan is knocked out), in which case he cannot play at all.
Seems reasonable, and it prevents from clanhopping, or clans that are in a final taking 4 superstar players from knocked out clans.