I predict a Goku "Ultimate" Edition.
They'll release one body, with four different heads (Regular, SSJ, SSJ2 and SSJ3) and maybe a few different faces and hands but not as many as the other ones. Maybe a ki effect or two but not much.
Business-wise, it's the best way to reuse those sculpts and still make major money since you'll be releasing a hard-to-find/sold-out sculpt (SSJ3 head) and a brand new one that people want to "complete" Goku (SSJ2). Plus, I'm sure people will pay a slightly higher price to get the whole set. I know I would!
Been watching GT for my first complete run-through (I've seen episodes here and there) and I'd even like a GT Goku as well! Both kid and adult.