#3. Goldberg is still a "WCW" guy

All said and done, the fact that Goldberg is a WCW guy still matters more than a lot of people realize. Think about this - Sting came to WWE over 14 years after WCW was brought out by Vince McMahon.
Even then, both opportuntities McMahon got, Sting wasn't treated right. Sure, you could make an exception for Seth Rollins since he was the hottest thing going in WWE at the time, but with Triple H, there was really no excuse for Sting to lose (and Scott Hall himself seemed bewildered by the idea that he lost his WWE debut).
In this case, it's a massive WWE legend vs WCW legend. While fans may think that WWE will let bygones be bygones, that's not the case at all. If anything, it only further cements the fact that The Undertaker will go over.