The trouble with rejoining is that the rest of the EU won’t want to let them back in with all of the same privileges and opt-outs they were once afforded. I suspect the single greatest hurdle would be having to adopt the Euro.

While many in the EU may be sympathetic and forgiving, I sense countries like Germany and France want to ensure the UK rejoins as a far more integrated and dedicated member state than they were before. It doesn’t seem like the UK has much bargaining power in any potential application to rejoin.