I see. If you don't mind, I'd like to give my two cents on BOTH of your ideas.
How DARE you!
1. Honestly, I'd actually wouldn't mind the idea of this story taking place during the little time-frame that we between Beerus and Whis saying their early goodbyes to F. Trunks and F. Mai and the Future couple leaving for the alt. future reality.
With Dragon Ball's fucking of screen time VS In-universe time, I can believe all this happening in one to two days.
2. The idea of this being Super's answer to the Bojack movie would also be something I'd like to see. Maybe this whole thing with Android 21 is SO severe, that F. Trunks feels that he has no other option available to him but to enlist the Dragon Team's help one more time. Don't forget, #21 is possibly in charge of the Dragon Team clone army.
You know, I'd love a reverse situation. For all this time it's Trunks going back to get the Z Fighters help, this time, let it be them getting his help. Or maybe have Beerus get Whis to go and get him "Okay, this shit got serious. Whis, get me that kid who has the power to make the fans rage!"
I doubt Super Saiyan Rage can handle THAT single-handedly.
Well, so far I doubt Super Saiyan Rage is gonna be in the game. Hell, Trunks isn't even a Super Saiyan 2... Or even have his Super design.