Don"t need it, plus ruled out.
Sounds kinda complicated to me, besides, sounds like it's a lot of programing SC will not want to do. Also, tracking & listing previous clans has been ruled out. All you have to do is scout one of the enemies bases, touch the clan castle, and see their actual clan line up to see if the new member is a spy. If he/she is, just kick him/her and tell everyone to change to a different base just before the war starts, or edit their existing to change the traps & teslas around. Clan Castle troops aren't even an issue any more since SC so "wisely" added dark spells like poison. They always have big hit point units like lava hounds, valks, or maybe giants, hogs, or surprise!, dragons. But mostly dragons.