I like the idea. In fact, I thought about it quite a few times too for the past few months...
Bad News Barrett, Ryback, Curtis Axel, and Justin Gabriel. That's it.
No need to bring Darren Young or David Otunga- too many cooks spoil the broth.
No need to include Heath Slater either, as his team 3MB is the only jobber team in WWE right now, but is much more entertaining than your typical jobbers, and does a fair job of making others look better while not making themselves look any worse.
Also, Ryback and Axel are so random right now, so to speak, and Gabriel doesn't even get used... So any proper role would be a plus for them.
The members are now much stronger and experienced than they were before:
Wade Barrett is now a lot more entertaining and believable tough guy, compared to the Bare Knuckle and Ruthless Leader gimmicks.
Ryback is always believable as a super-strong powerhouse. Just have him bring back his ShellShocked finisher. He is also the only one among the group to have main-evented two PPVs.
Curtis Axel is a former IC champion and Paul Heyman guy. He can serve as the team's slightly weaker link, but that won't matter, because most of their acts will be ambushes anyway.
Justin Gabriel is a talented star who unlikely didn't have any story written for him by creative. He can go back to doing the 450 splash, and can serve as the team's high-flyer (like Rollins is for The Shield).
Titus O' Neil is one name that just came to my mind. Lets face it- his current role isn't one that you'll see main-eventing shows... So why not put him into the stable too? His muscle and size can help make the Nexus a more legitimate threat for everyone else.
And the most important thing to do, if such a reunion happens, they should be kept away from people like John Cena and CM Punk. They can be used to push the other stables like Shield and Wyatt Family, maybe the Usos too, but certainly not wasted on stars that have already reached the top but still have a tendency that is not-so-likable.