I'm no expert on the film business, but I know enough about this stuff to burst some bubbles for Arrested Development fans if the reaction I saw in a few places to news that a script was in the works is indicative to general sentiment.
So what the hell does that even mean? Put simply, just because a script is "in development" with actors "committed" doesn't mean a movie is imminent.
Not even close.
Hundreds of movies reach this stage per year, maybe a thousand for all I know, because it's relatively cheap to pay someone to write a script and consequence free for actors to "commit" themselves to a movie they want to be in, in spirit, but that's entirely different than signing a contract. If this movie were imminent these people would be locked up by contract so that they'd be available for production and the script would already be done by that point.
Depending on who owns the intellectual property of the show, this could be nothing more than a spec script being written with the hopes of enticing the the studio to bite. But even if that's not the case, people are paid to write scripts to flesh out concepts all the time.
I've never seen Arrested Development but I'm sure it was a great show and I appreciate that a lot of fans are hoping for a movie to follow. That's great, and I hope they get what they want. Just don't get your hopes of because of this. The only stage at which you should get excited is when you read that a date for principal photography has been set. 99% of all movies die in between now and when the money has been committed to sign talent, and that's where this project is sitting today.