Yeah that's a great theory, Freeza is either going to help him or ask him how he did it I think. They already baited Freeza's betrayal so I don't think that'll happen now unless it's the end of the tournament and he turns on them to get the wish.
Freeza is shown to be very intelligent so he knows he can't beat Jiren and if he is setting up betrayal, it won't be a suicidal executing of Goku now, it'll be having him and Jiren take each other out.
I belive the endgame, given the tone of the series, will be all the erased universes being merged from a Super Dragonball Wish or King of All hearing a plea from Goku to do it. In that case I think having Freeza still be around for future arcs/series will be more interesting.