I'm torn, but I will say this in Marcelo's defense . . .
First, he takes the back like none other, but no one is debating that. Also, i am a big fan of the X-guard and have been working on it a lot recently.
I've also felt the X-guard of good grapplers, and so I can say from first hand experience: It's hard enough to just be standing when a good grappler has X-guard on you, let alone to wind up and throw a punch, sacrificing your base in the process. All the best grapplers on earth do their damnedest just to keep on all fours in Marelinho's X-guard. How many people in his weight class have good enough base to stand there and drop bombs on him, esp. when he's got them doing russian splits? :icon_twis I'm not saying he'll just smoke dudes by playing from the bottom, but I don't think the X-guard will get him in as much trouble as some might think. Also, the list of guys who can put him on his back is not long, but if someone like Sherk did, I think Marcelo would be better off playing X-guard then full guard (esp cause Sherk's short arms couldn't reach that low - J/k).
Also, let's not forget that he's not even that big for his weightclass, and with work he could definitely fight 155. Granted this is a new class for the UFC without too many big names, and though it would be quite a fight between him and Sherk, the class is small enough that they could each share the spotlight, smoking other competitors and building the tension, for a while before clashing for the title.
Also, unless you are a big fan of his, you may not know that Marcelo got involved with BJJ specifically because he wanted to fight MMA one day. Though he is a nice, quiet guy, he's got what it takes to train like a machine and be a top fighter.
Despite all that . . . Jacare is a Monster. At 185, I doubt there are a dozen guys on earth who could out perform him for sheer physical strength, conditioning, and athleticism (he looked like he weighed 210 when he rolled with Randy). His speed and power are easily comparable with fighters like Franklyn (superior IMHO), and he could obviously eat Anderson Silva on the ground. I think that after a good handful of fights, he could be ready to handle the striking of someone like Silva long enough to force ground action. From there, let's face it, the guy's a finisher all the way. Too bad it seems we won't see him in the UFC!
Sorry for the long winded post. I hope I meet with much disagreement, i love a good argument :icon_chee .
cheers.