Well, this wasn't what I was expecting.
I get where you're coming from. You already have one title on the line, and the other two singles title holders are in contention to win it. Putting all the straps on one guy would be a huge deal. In kayfabe, bigger than Rollins winning the US title from Cena at Summerslam, and bigger than Warrior's win over Hogan at Wrestlemania. But, that's kayfabe.
The two issues with this hypothetical are the people involved and where they go from the win. Del Rio isn't over nearly to the point necessary to carry all those belts. And the belts wouldn't make him either. He has a disconnect with many fans that just can't be bridged with wins and losses. Owens is over, and I could see the case for him, but then what? He goes on and defends 3 belts all the time? Or the other two minor titles dissolve into the WWE title and there is only 1 belt? Either way, it's too much for one character to take on.
Even if you switch the guys around, and have Reigns and Ambrose in there instead, it's too fast to make this happen. No build. No hype. Just a sudden, oh, yeah, by the way, all these titles are on the line. And then what? One guy gets made big time and the others are stepping stones along the way. That's the problem. When Jericho beat the Rock and Austin, he beat two huge names. If any of the four guys in this tournament beat the other three, they'd be beating some mid carders, a guy who didn't win a Wrestlemania main event, and Alberto Del Rio.