I think the possibility of it has definitely grown since Orton's return, his pursuit of Rollins and Lesnar waiting in the wings to exact his rematch clause.
If this match does take place, I'm of the opinion they should keep it simple. Randy Orton's never been portrayed as a "nice guy", Brock Lesnar isn't a "nice guy" and has never been portrayed in that light either. As a result, ultimately keep it as something along the lines of a couple of predators, The Viper vs. The Beast, fighting over the same carcass, AKA Seth Rollins & the WWE World Heavyweight Championship. Which one is really the Apex Predator? Which one is really King of the Jungle? Or whatever tag line you want.
I think it could generate a lot of interest, though I do think having the title involved could hinder things a bit. After all, let's say that Lesnar is champ by the time he & Orton have a feud, you could have what MIGHT be perceived as a lose-lose situation if the title is involved because a LOT of people are tired of Randy Orton being World Champion, probably as much as they're tired of seeing Cena as World Champion. It all goes back to Orton & Cena being booked so consistently for such a long time in the title picture that a good number of people are burned out on it. As a result, you'd no doubt have some who'll complain that this would be a wasted title defense for Lesnar as he only comes around every so often. It's lose-lose for said fans because either Lesnar retains and it'll be another 3 months or so before he defends again, or Orton wins and they're stuck with someone that's champion, yet again, that those fans simply don't want as champion anymore.
As a result, I'm of the opinion that it shouldn't be for the title, maybe more like a #1 contender's feud to see who goes after Rollins next.