I know I am very late but I've been watching DBS Broly again looking for small details and I have a bit of a theory it has possibly been said before but I wanted to put it out there just in case it isn't a big theory that is predicting the story it is just that in the movie while Broly is toying with ssjg Goku you see his pupils disappear which is db's way of showing when a character snaps/gets really really angry and just a few seconds after you see gokus ki go green so I was thinking that next season's transformation would be that Goku/vegeta goes into the same form as Broly (don't know the official name for it).

PS. I say "next season's transformation" because if you look at every season of DBZ and DBS to date there is a new transformation that has never been seen in the anime.