Ah dammit, I was gonna make this thread.

For some reason, the notion of them adding a third member just popped into my head a few minutes ago.
At any rate, I think it's possible. In Triple H's latest in character interview with Michael Cole, he says that The Shield doesn't exist anymore and said the reason he chose Rollins was because he was the thinker of the group, the brains of the outfit. The fact that Trips has outright stated that The Shield no longer exists translates into The Shield is still around, the feud will continue and he expects to decimate them since they've not only lost a member, but they lost the "brains" of the operation. In a 3 on 2 feud, with 1 of those 3 being a founding member of The Shield, Ambrose & Reigns are at a big disadvantage. As heels, they played the numbers game quite often to help get themselves noticed and their chemistry made them a force to reckon with. Now they don't have the numbers and they can't have that same chemistry.
I don't know if they should get a third member. For or against, there are good arguments to be made. It's an opportunity to possibly elevate someone from NXT right from the start, a means of getting them noticed and part of something relevant immediately. Hell, for that matter, it could be an opportunity to repackage someone already on the WWE roster, giving him a fresh start. At the same time, there's no guarantee that new member will gel with Ambrose & Reigns the way Rollins did. Chemistry is something that some people have and some people don't, it's just how it is in pro wrestling and life itself. Also, they shouldn't just add another member to the group just for the simple sake of keeping things even. The new member
HAS to be someone that WWE officials believe in and can bring something unique to the group. A huge selling point for The Shield was the fact that they each brought different qualities, useful qualities at that, to the table. A new member must be able to do that, otherwise I don't see it clicking.
It could be an uphill battle. The original Shield was a fantastic unit, it'd be like The Beatles trying to replace Paul McCartney or John Lennon. Finding someone who can be both different than Rollins in some way while still being able to do a satisfactory job in his spot and add something unique to the group may not be easy.