Personally, I think adding him to the series and the other villians answering to him through out the series would be far better leading up yo the next movie and it flow through the games as well because the reasons given for him not being used seem like even more reason to have him otherwise he just seems relevant only for movies and not the grand scheme of things. It would essentially make him look like the powerhouse that he is having him in all 3, the movie, the game(s), and the series. I base this off of other series and movies past and how it was delivered and received and did far better than not being completely part of the lore or cannon and the character was nurfed/minimized to not be the true big bad of that portion and powerful enough to do mote than originally imagined, such as being able to leave the realm and travel to other realms and then some.

Considering they had him in the beginning of fast 10, even though it was a recap of Rio, they should finish the franchise with Brian helping this final time to bring it full circle, paying respect to not just the character but the actor as well. I believe his brother was in the beginning of 10 even though it was slightly different but pulled it off flawlessly.