I know that the rumors are that these two will be involved in the two World Title matches, but wouldn't it make so much more sense to use them to build new stars? I know, I know, Vince doesn't believe in that. But it's such a simple story: Brock makes a return in February or so, demands a title-match at WM, Keith Lee or Big E interrupts and tells him “no, you can't just show up once a year and cut the line”. Boom, that's all you need, now one of them gets to beat Brock at WM in a big match and you've made another star. And whichever one of Keith or E doesn't interrupt Brock gets to eliminate Goldberg from the Rumble. The opposite works too, one of them eliminates Brock from the Rumble, and the other interrupts Goldberg. Whatever. This is about as obvious as it gets.
Or they could just stop bringing them both back and worry about building their own stars for a while. Either way.