late reg will just make tourneys re-entries for the multi accounters
so this is a legitimate concern.
As a frequent MTT player, I'd like to see the biggest prizepools possible.
As a site pro, I don't want to see anyone just miss the start of the BIG BTC.
I think the sweetspot for late reg is ~5-15 minutes. I want to catch the guy that just missed it, but I don't want the guy that just busted re-registering. Very few players will bust in the first 15 minutes, and those that do should be easy to catch a re-entry under a little-used account.
Certainly things to think about, but IMO late registration will be +EV for the players, as it encourages action.
Late entry for rebuys is a no brainer. That will work. For what that's worth.
Without blocking IPs and disallowing tor (not even possible?) I don't see a solution for regular tourneys. In that case if you want late entry you just have to deal with the reality it's a rebuy for shadow accounts.