I think they'd make a good duo. They'd be somewhat interchangeable, with Haha being a better enforcer, and Randall having the coverage and ball skills necessary to be a solid centerfielder.
"Interchangeable" means the guys can play either position, as with Burnett and Clinton-Dix. One game last year, I noticed they alternated coming up in the box and playing single-high...tick, tock, one for you, one for me...to what end I'm not sure. It wasn't very confusing to the opponent. Maybe Capers likes to alternate the hitting and the sprinting to keep the guys in some balance of fresh throughout the game. In general, it gives you more flexibility in the event of injury when the #3 is strictly either a FS or SS type.
Randall's not a guy who could come up and stick his nose in against the run. Then again, neither is Brice. I agree that Randall is strictly a centerfielder. But if you wanted to mix up the look, you could drop Burnett pre-snap and bring Dix up. This of course will never happen for a couple of reason.
First, it's not like we should expect Burnett taking 40 snaps in the box this season. Yes, McCarthy said he wants to use him more at ILB, but I'd expect that to be something in the overall mix, how much based on the week's matchups. He'll be taking a lot more snaps at S to be sure unless everything starts miraculously clicking.
Second, Randall was a first round pick for cover corner, and gosh darn it, that's where we're going to teach him to play until we die trying or 4 years elapses, whichever comes first.