Yeah, that could work. Although I'm tempted to say leave in the use of the Gokai Machines since so many modern Sentai mecha have so many various combinations. Even with the Gokai machines I'm sure they'd struggle in a 2 against 4 scenario with the Go-Onger robots
I would for the Gokaigers limit them to one alternate team to change into if we wanna be fair. Like they can't be who they fight and we randomly select from one of the other teams to change into. Greater Powers limit to GoJyuJin and Machalcon in terms of powers since they are part of Gokaiger's final Mecha