For me personally, I'd rather they just did this match at Survivor Series and get it out of the way. This is a match designed for those who're casual to average viewers and those viewers who're in the mood for a nostalgia fix; that's all well and good, Goldberg vs. Lesnar will probably be a good draw, but those of us who know better know not to expect very much out of this match.
As far as conditioning goes, Goldberg is entirely up in the air as the man hasn't wrestled in over 12 years; if history teaches us anything, however, it's that this shouldn't be a long match as Goldberg certainly wasn't much in all that matches than went to or beyond the 10 minute mark. Goldberg looked like a badass and had a tremendous look, but that's about all. Brock Lesnar used to be an athletic dymano, a freakish combination of size, strength, speed and overall athleticism that made him the living incarnation of Vince McMahon's ideal professional wrestler. Lesnar still has a ton of raw power, but has retained very little of that remarkable athleticism and stamina that helped him become so dominant and leave such a lasting impression in the roughly 2 years he was in WWE before leaving for a decade.
If this match lasts the 15 minute or so mark, I don't see either guy doing a ton of stuff beyond the standard offense. Lesnar is gasping for breath usually about 10 minutes or so in, is sweating like a sinner on Judgment Day and turns about half a dozen different shades of purple; there have been times when he's so gassed that it looks like he's about to pass out in the middle of the ring. I've read that he does have some sort of respiratory condition in the past, I don't know if it's true or not, but, if it is, then maybe that explains it because otherwise the guy's just flat out lazy.
The layout of Survivor Series would indicate that most of, if not all, of the champions for all the brands will be involved in traditional Survivor Series tag team matches. If that's the case, then I'm all for Goldberg vs. Lesnar to take place as sort of a special attraction because I personally don't want to see this feud eating up tons of airtime as part of WrestleMania. Then again, it wouldn't surprise me if Vince decides to book a rubber match between them if Lesnar goes over in this one because that's been a frequent formula in how Lesnar has been used. There's still hope, however, as even if Lesnar wins, the match itself might be so lackluster that there's no real interest in seeing a rubber match.