There seems to be some confusion about the difference between the weight that a fighter "walks around at" and the amount of weight that a fighter cuts. There are fighters who will come into a training camp weighing 15% over their fighting weight (in the case of Anthony Johnson, there are reports that he's at much as 25-30% over when he starts camp), but rarely do fighters cut more than 10% of their body weight on the day of the fight.
I strongly disagree with this proposition. While many will look at the likes of Shane Carwin and Brock Lesnar and use there obvious size advantage over the likes of Cain Velasquez and Junior Dos Santos as "proof" that there is a need for a split of the HW division. I take issue with this fact based on one major facet obviously being that despite a huge increase in recent years the sheer number of legitimate HW's running around that would compare to the size of Carwin or Lesnar are few and far between. This number drops substantially when you star taking weight cutting into account. Big LHW's are walking around at 235+. Thiago Alves cuts from over 200lbs to make 170 that is 30 pounds of weight cut and yet when he fought Fitch he was the smaller WW of the two. If the likes of Fitch and Alves can lose 30lbs than you have to assume that HW's like Lesnar could do the same. Taking into account the 200lbs a guy like Alves, Fitch or Anthony Johnson would walk into the cage at then your looking at them cutting about 15% of there body mass. Using this index and assuming all things are equal then a guy like Lesnar walking in currently at 265 pounds would have a easier time cutting the 11% that they would need to lose to make 235 and maintain the size advantage they currently enjoy.
If someone like Brock Lesnar wanted to cut to 235, he's welcome to give it a try, but I'd hazard the guess that his camp would say its simply not possible for him.
Cain, who comes in about 250 around fight time nowadays at heavyweight, would have an easy time, as he'd have to cut well under 10% of his bodyweight. The same is true for guys like Dos Santos and even Cheick Kongo, who are borderline.
It also lets those larger lightheavyweights who couldn't contemplate stepping into the heavyweight division before, because they'd be giving up 50 pounds, (220-230 at fight time vs. 275-2980, which is not uncommon in the current heavyweight division) step into a division where the most they're going to be giving up is 25-30 pounds, an advantage that we've seen in middleweight and welterweight fights before.
Actually, just so we're clear on the numbers, 15% of 235 is a little over 35 pounds. If you maintain that fighters can cut 15% of their bodyweight then they could, theoretically, come down from 270.
If we are looking at This leaves you looking at who would really be forced to fight in the 265lb division. Using the analogies of some of the bigger fighters in other divisions we have established some of the larger cuts are up to 15% body mass which means even a 276 pound fighter could in theory make your new found cruiserweight division.
By the way, that excludes both Brock Lesnar and Shane Carwin (not to mention plenty of other true heavyweights) who come into camp at 280.
I don't doubt, actually, that Lesnar or Carwin could find ways to lose the weight and make 235. I seriously doubt that they'd want to. The amount of cardio that it would take out of them to make that weight, the amount of strength that they would lose, would discourage that cut enough.
See, I doubt that.
Using this logic your new found cruiserweight division basically becomes the current HW division with the only difference being that these larger men are now cutting weight which only leads to further hurt there cardio. Does a group of fighters where good cardio tends to be the exception and not the norm really need to further stress these guys bodies? The only losers here would be the fans. The current 265 pound division would end up filled by either the talent lacking current SHW division or by those to lazy to get into appropriate shape to make the cut.
There are a substantial number of true heavyweights who have no interest in cutting to 235, and who probably physically couldn't anyway without serious health risks. Lesnar and Carwin would certainly be left before, along with many of the other true-heavies. Now, the problem is that there isn't a whole lot of good talent in that division. That's a real obstacle, but it's not insoluble. The UFC needs to recruit better in that division anyway.
The cruiserweight division, though, would get really exciting, really quickly. You get Cain Velasquez in there with most of his serious competition, and you have the opportunity to actually have lightheavyweight come up and challenge guys in the heavyweight division.
There's discussion about getting Jones or Machida or even Anderson Silva to fight a Frank Mir or Cheick Kongo. That only happens in the cruiserweight division. It never happens in the open waters of the heavyweight division where the smaller guy isn't guaranteed an opponent of predictable, reasonable size.