I'm liking the idea of somebody holding both the briefcases at the same time, however, I would argue that the idea of the person proceeding to go on and unify the belts would be counterproductive towards the company as a whole. We can all pretty much agree that the WHC has lost most it's credibility over the years, but there's still the opportunity to bring back some of the credibility it once had, how/when you end up doing that is almost irrelevant because with one feud it could become the most important title in the company.
That being said, during the "Mr. Dual Money in the Bank" reign you could have them pushing the idea of him unifying the belts so they can reign supreme as the absolute pinnacle of WWE, but that would suit way better for a heel than a face, a face being what I would prefer writing for if I were the one writing this situation. It would be a really good opportunity to push someone BIG and get them up (and possibly beyond) the top using the simple "Yes, I am THAT good" style of getting someone over, a style I am particularly fond of. Think of it, someone winning not one but TWO multiman ladder matches in one night?? That's insane! Whoever manages that should be treated like a damn big deal, after that night they would have to win the majority of their matches pretty dominantly and they would have to continue to keep climbing the card at an accelerated rate, to the point where there would be no one left except the very top stars. The question that remains is who do they currently have that could deal with this much exposure and continue to grow? Honestly I think they've got two choices: Daniel Bryan or Dolph Ziggler, and personally if I were writing it I'd go with Ziggler.
Yeah I know it sounds crazy, but I'm serious, if they're going to push someone to the freaking moon like this I'd put Ziggler in that position, and I'd have him go over some damn big people too. I'd have him barred from competing against Del Rio at MitB due to his head issues so instead he finds a loophole due to him being only barred from competing against Del Rio, not from competing altogether and manages to win both the briefcases - stealing the show, of course. now here's where I go to the crazy parts of the story, the night after on RAW I'd have Ziggler do a promo about how now he can now have two shots at getting back his WHC because he is just that damn good, but in the middle of the promo get assaulted by the Shield saying that his dual win is an injustice and so forth. then next week I'd have Ziggler come out again this time talking about how he is now just that damn good that he could take on the Shield now because this time he's ready. The Shield would then come out to attack again but this time Ziggler fights back, he almost clears the ring but a spear from Reigns takes him down but then here comes Daniel Bryan and Kane for the save, setting up some form of tag team match at Summerslam between the two trios (preferably a table elimination match or something like it) with Ziggler getting the win and standing tall. Now, during these timelines we're assuming the Brock/Punk feud is going to culminate at Summerslam, with Brock winning to the internet's dismay. RAW after Summerslam Paul Heyman and Brock are in the ring with Heyman talking about how their savior CM Punk couldn't stop Brock and that nobody can in the WWE. Cue Ziggles to come out and say he's the dual money in the bank holder, he's the guy who beat the shield, and that he's the one who's going to beat Brock Lesnar because he's that damn good.
You know where I'm going with this, I'm having Dolph Ziggler be the one to defeat Brock Lesnar on PPV, and it would be glorious too. It doesn't end there either, Ziggler still has two briefcases, after the feud with Brock I'd have him come out to say he'd like to have his WHC back now in a match against Del Rio at the next PPV using one of his briefcases. The match would be pretty one sided towards Ziggler with him dominating most of the offense, but in a twist Del Rio would grab a sneaky DQ to win the match, pissing off Ziggy and forcing him into an uncontrollable rage beating the crap out of Del Rio using chairs, tables and even the briefcase to brutalize him, before handing over his OTHER briefcase to the ref, capturing the WHC and ending the PPV as the new dominant heel WHC.
There you have it, my way of using two briefcases to elevate Dolph freaking Ziggler to the top of the card and give the WHC credibility. You could do it with Daniel Bryan too but the baseline of "He's THAT good" still works pretty well as you still end up with a ruthless aggression style heel who has the credentials to beat anybody on the roster.
Other ways to get rid of the briefcases if one were to win both would be:
- losing one of them
- winning one title but losing the other
- winning the title and using the other one to win it back after a dodgy loss
- losing a briefcase and using the other to get it back i.e. briefcase-ception
- winning a title with one and winning the tag titles with the other