4 Rooks might have a chance if they can farm up enough xp for their base HP to get crazy.
Maybe Two Sednas with level 1 Priests and Two Rooks all stacking HP would have a chance. Do multiple healing auras stack?
You could go a totally different angle and make a pushing team that tries to kill the enemy citadel as fast a possible instead of actually trying to kill enemy DGs. Two Rooks going stats/tower drain and two QoTs going Bramble Shield/whatever the siege move is could potentially cut straight to the citadel. Rooks would spend gold til they had at least 4k hp and a helmet or two, then the rest of their gold would go to Citadel upgrades, especially creep upgrades. QoTs would get Level 1 Priests to start, followed by HP to 3-4k , and then possible the max level Siege Archer idols to speed things along. After that all their money would go into the Citadel as well.
These are just three ideas for teams that could potentially counter 4-Reg. Note that 4-Reg requires almost no organization or pre-planning, while one of these teams would.