Here's the thing with Green Lantern, if you're looking at it from a studio point of view:
They're not looking so much at potential as they are connectability. And the story of Green Lantern, while being open for all kinds of interesting cosmic fantasy action, is also one of the more inherently goofy premises. A giant lantern from space that recharges a celestial battery held in a ring that makes your every imagination come true, but only works when the color yellow isn't up against it? And putting the ring on automatically enlists you into a society of intergalactic police?
to suits, while the concept predates these movies, it's going to sound like a cross between "The Mask" and "The Last Starfighter." Yes, I know, a traumatized child dressing up as a bat and an Alien landing on earth and wearing blue leotards ALSO sounds goofy when you reduce it to it's base elements, but Green Lantern is pretty out there. Plus, honestly, the name is pretty inherently goofy as well.
And those are two movies that weren't known for their gravitas, yunno?
To the moviemakers, trying to figure a way to get this idea across onscreen, to neophytes (who they're aiming for) the idea of playing this utterly straight faced HAS to be scary, because the elements are SO fantastical and lacking mythical allegory, for the most part, that it's almost automatic that there's going to be some tongue-in-cheek in addressing it. That might be the best way to have people buy the concept. After that, then they can try to mix in some of the more mythic, serious concepts, but it's a "Spoonful of Sugar" mentality, I'd believe.
So keeping that in mind, I can see why they'd want a more lighthearted take on the concept, starring a known comic commodity.
And like I said in the interview--he doesn't look BAD in tights. It's comical, yes, but he's not like slovenly fat spilling over the spandex. I'd think Warner's would get him to drop SOME weight, enough so that a creatively designed suit would cover any shortcomings in his body type.
Keeping all that in mind, plus the fact Jack Black has proved to the suits in Hollywood that he CAN handle serious if he needs to, it makes sense to me that Warners would have tapped him to head up this version of Green Lantern. The character simply isn't popular enough or well known enough in the public as anything other than a sidekick character (if he's known at all) to mandate slavish adherence to the core of the character in his best iterations. It's why I said, semi-dismissively in the interview, "It's Green Lantern, man." There's just not enough pull with that particular character. Hell, the myriad numbers of main character switches works AGAINST it in this case, because a suit is going to look at how many different people have been The Green Lantern in the comics and say "Well, if he's changed identities THAT many times, why not one more?"
