What about a "Trainer Mode":
- game lobby contains checkbox for trainer mode
- at gamestart the trainers acus are set to invincible, not producing resources, build paused and teleported offmap
- when the last non trainer acu of a team dies the trainers acu will also die
Imagine casts / streams with several trainers for one team!
Also the trainer / trainee tournament would be much easier to setup.
The technical alternative would be to make an observer based trainer mode where you select also a team. The view is switched at beginning to a team member and cant be manually altered but is only changed automatically.