Could do like some other games, and have an official team charter for premades. Changing out a team member for a new one will cost you team rating. I think one of the problems with premade teams right now is specifically that SE has it set up to allow a single person on a team to jump ship anytime they want and boost themselves and screw their teammates. How many of the data centers have a team of 4 people ties for the number 1 spot on party ranked? None. Chaos has 2 people who have stuck together for the entire season, meanwhile Aether has a single person sitting at 600 points higher that the second highest person from ANY data center.
Team Feast needs to be about the team, and it isn't right now.