I'd Definitely say Adult Goku, Since Dragon Ball Z Specifically is the Most Iconic part of the Brand, as well as the fact that he can use all the Transformations more than Kid Goku can, even taking into Account GT.
Now I would want to say that since you Got both Akira Toriyama and Bandai Namco on Board with Smash already (Akira with Dragon Quest, and Bandai Namco having the Game rights to the series) that Goku can be in prime position to break the "Non Video Game Rule" but it might seem like it's not the case
Dragon Ball editor Akio Iyoku resigns and says he will keep the license for his new company Capsule Corporation Tokyo.
en.as.com
www.kanzenshuu.com
www.kanzenshuu.com
Shueisha seems to be the Ultimate rights holder of Dragon Ball, but It seems currently there were some Negotiations about the rights since the Chief editor quit from Shueisha and seems to have started his own Capsule Cooperation.
All Toriyama can do is sit on the Sidelines for now, so as Much as I want it to happen, I don't think Goku is in a good position to break this Limit. I actually think the character right now most likely to do that is Mickey Mouse