I completely disagree. They have already waited far too long - and since they never threw a real swat at Spiderman, they kind of are way behind already in inventive/impressive attractions in Florida.
I'm no Potter fan (I read the first few chapters of the first book and gave up in disgust because I really didn't like wimpy Harry - I was like - smack those idiots making you live under the stairs) and I'm a casual fan of the films (I own none, I still haven't seen the last two) so I'm not really biased towards the franchise.
That said, like most, I am wow'd and awed by WWOP. Even if you don't know anything about Potter, it's a masterful area. And it will be a long time before we ever get a ride that successful and immersive at WDW. I hope we do someday, but it will be a far, far bit in the future I am afraid.
While the franchise is important, it's not the be-all-end-all. Back when Star Tours was added, Star Wars was kind of in "remission" (no new product for years before and after), and it wasn't until the mid-90's that figures and merchandising really came back into full swing. There weren't even tie-in books to speak of until several years after it opened. I also don't think J.K. Rowling has left behind Potter as much as she would like to think, or would have people think - she has created an incredible world that has limitless possibilities of stories, I wouldn't be surprised if we see books about Harry's children or other characters before a great deal of time has passed, with Harry himself becoming an "Obi-wan"-type character.
That's the one argument that I can give people who are Pro-Avatar - that even though I don't think much of the "franchise" (it doesn't really exist yet beyond one film, and has largely already left the public consciousness) they still could make some awesome theme park attractions out of it. Thing is, since Disney doesn't really go that extra mile with attractions these days, if it should actually happen I have a feeling the "big ride" will be a pseudo-Soarin' clone (perhaps with a more immersive screen that goes below you as well) and a few practical visuals, a themed meet & greet, some stage show with video screens and 3-D, and some sad eatery trying to "tie in" with blue juice or some other silliness.
Truth be told, Cameron is kind of delusional if he thinks the next film will even approach the first one in terms of money - that film was a massive hit because 3-D was new and it was the first film to really use the technology to it's fullest extent. Thing is, even die-hard 3-D supporters who even just a year ago insisted that it was going to take over and every movie would be in 3-D is already admitting it's started it's regression back to a fad state as many of us always knew it would. That's the key difference between the two - and unless Disney really pulls out the stops, if they do follow through with Avatarland, I just don't see them actually doing more than making a feint wind in the direction of Universal, nothing near capable of swatting Potter as the best theme park attraction around. I mean, they never topped Spiderman, and it seems they are content to not top WWOHP unless they really start spending some big bucks NOW - on more than just fancy new fastpass systems and "virtual games".