Thanks to the Heroes Victory Mission manga chapter 28 I was able to learn which of the two transformations that Beat and his Saiyan avatar friends will use in the future. As a summary of the chapter that concerns Beat it goes like this:
"Beat and Sora continue to train in the "white room" so that Beat can have the strength needed to battle Legendary Super Saiyan 4 Broly".
As you can see he is TRAINING alone with Sora(Galaxy Mission Beat look-a-like). As we can guess that the "white room" is the Room of Time and Space. Beat is going to be training for a whole year to get the power needed to fight with Broly. Now you can guess what the transformation is due to these elements. Had Beat and the rest of the saiyan avatars accompanied Sora to the "white room" then we are sure it would have been Super Saiyan God because it requires 5 pure hearted saiyans to give their power to 1 pure hearted saiyan so 6 in total. But because this is not happening the only other transformation that doesn't require all of them together plus they meet the requirements is Super Saiyan 4. And since this chapter was released soon after the announcement of God Mission set for Dragon Ball Heroes then you can guess what Dimps decided to go with. This is going to be a monumental moment for us fans for we get to see the unveiling of Dimps' official version of a Female Super Saiyan 4.