[Nowhere Man]

Not that it contradicts any of your main points, but most of the well-known superheroes were only isolated in their own separate worlds for the first very few years of their existence. National Comics and their subsidiaries (which would eventually become DC) were putting all of their flagship characters together in the Justice Society, and Timely Comics (the precursor to Marvel) was putting together the All-Winners Squad, both during the height of the Golden Age in the 1940s, a full two decades before the Justice League or the Avengers. While the later teams definitely solidified the idea of pooling the continuities together, it was hardly a brand new idea.

As for the main meat of the article, while I can definitely see the huge money-making potential for studios to lean towards making one big movie-verse, it does create a lot of problems in terms of consistency, continuity, and quality.

For example, if we're going to tie Nolan's Batman series to the upcoming Superman reboot, there's the simple problem that Superman was apparently just sitting on his ass letting all of that horrible stuff happen to Gotham City--seriously, name one thing that the Joker or Ra's al Ghul did that Superman couldn't have put a stop to within a minute of showing up. Sure, you could say that he wasn't Superman yet, that he was still in pre-tights Smallville mode, but unless they're going to just completely gut the character of his core principles, Clark still would have made the effort to head that way and lend a hand. The only way the Nolan movies work in relation to the rest of the DC universe is if there is no rest of the DC universe, that Batman has to save Gotham by himself because there's no one else to come in and help him.

Another problem is one that used to frustrate me to no end about the comics themselves: that half the time you can't tell what the hell is going on in one story until you've seen all these other ones first. Marvel's recent Siege event was guilty of a lot of this, and don't even get me started on DC's Final Crisis and Blackest Night. If you're planning on using already established characters to team up for a major story, then you have to run on the assumption that everyone has already seen the movies establishing them, and that will cost you viewers who didn't see the other ones and don't feel like doing their 'homework' (I still have plenty of friends who never saw Dark Knight because they didn't see Batman Begins first). If you're going to introduce new characters into the mix, then you have to waste valuable screen time on their origins rather than fixate on the central plot.

Finally, and this one is entirely just me, but I cannot imagine the script for such big team-up movie not being total shit. Yes, there are several great stories in the comics that involve almost the entire Marvel or DC universe, but most of those arcs were told across several issues, where the author had plenty of time to flesh out whatever he/she was trying to get across. In a movie, you've got about two hours, two and a half tops, before the audience loses patience. Creating a conflict big enough to get all of those superheroes together, writing each of the characters to convincingly react to one another and to the situation at hand, keeping the narrative engaging and entertaining, and still keeping in enough big-budget action to give the audience what they came for, is no small task. In the end, I have no doubt it will be big and loud and explosion-y and make a godjillion dollars, but it will likely come at the cost of the movie itself being stupid as hell.