Forget it, the multilog/proxy war is lost. No point flogging a dead horse, really.
Just try to enjoy the game as it is

With relogging in combat and armies of alts farming quests

Or make a FOnline server with invitations, then you won't have cheaters. But most likely you will have empty server.
Your proposition wouldn't even help with proxies in PvP. If they stand doing nothing they do this on WM.
It would be just annoying for people who don't proxy and like to idle.
So it would be like DRM - not a problem for pirates, pain for people who buy legal games.