Nothing is confirmed, but they showed Goku vs Frieza in the trailers and I doubt they’d show off the final boss, even if it’s a battle everyone knows of.
They’ve said multiple times in interviews that this game is about “experiencing Goku’s life through the Dragon Ball z anime,” and have also mentioned that they made a system for how transformations (explicitly plural) will work in the game. If the game is just up to Frieza, the only transformations are Kaioken and Super Saiyan 1 (which you’d only have for the final boss), and those are just Goku.
If you include the Cell saga, you have Kaioken and SS1 for Goku, SS1 and SS2 for Gohan, and SS1 (and maybe the ascended levels too) for Vegeta and Trunks. Still multiple transformations, but only one or two per characters.
If you go all the way through Buu, you have Kaioken, SS1, SS2, and SS3 for Goku, SS1 and SS2 for Gohan, SS1 and SS2 for Vegeta, in addition to any forms needed by potentially playable Gotenks and Vegito. That sounds more like something that needs a transformation system.