So it is going to be Equius who enters first after all. Furthermore:
If he and Vriska are in cahoooooooots, then that suggests that he plans on bringing her into the Medium himself.
We know already that Sollux will be the last member of his team to enter the Medium, but the flash forward to him waking up didn’t actually specify which team that was. My guess is that by the time he wakes up, Blue team will have completed their chain and he’ll be stuck on the Red team with Karkat as his server.
Vriska <– Equius (first to enter) <– Aradia <– Nepeta
Sollux <– Karkat (first to enter) <– Terezi <– Gamzee [Possibly]