What are the chances that WWE swerves us with Brock cashing in on Kofi at Stomping Grounds? This could lead to a SummerSlam rematch with Brock retaining. (Despite all the potential groans, Fox's SmackDown needs him as champ for name value).
Meanwhile, Seth can carry on for months about how Brock is a coward who ran away from him. Then, when WWE finally ditches the wild card crap and unifies the belts at Mania, it's Brock vs. Seth, finally, for the Universal WWE Title.
Not that we don't already have enough fantasy bookers or 50 WWE writers, of course…
Yeah, I think Kofi is the better heat because Brock can be the guy to crush his dreams and as you noted, it establishes that Brock is a coward who won't face Seth despite multiple chances to do so. That being said, they've undoubtedly used up ALL their punches on the Brock Lesnar Card until Summerslam, so I doubt it'll go down like that. But the idea of getting Brock as champion before the FOX launch is probably the correct thought.