Just like the thread for the new muppets.com, am coming to this one later in the game (you can see my commments in that other thread as to why) but at least this way i can comment on different things that have been posted so far and throw out some things that haven't been touched on as much yet.
My gut feeling is that the press release was issued the way it was as very strategic - get both the buzz going in both the show business and the fan communities, hoping that once that gets rolling than it gets harder for Disney and Henson to turn down the chance to be involved.
One of the first things they teach is you in directing classes (well at least the thing i was taught, can't say if all other teachers emphasize this) is that the main thing that will make or break and have the most influence over all other aspects of the production is casting. Personally, i would really take the time to get this right and not limit it to big names. I would actually start by putting out casting calls within puppeteer groups or unions as who knows how many skilled puppeteers out there (that don't necessarily have any relationship with Henson/Muppets) are also skilled actors...you may not find your Jim, but you may find your Dave or your Kevin etc. Steve absolutely would NOT play Jim, he's gone on record too many times about he's very shy in front of a camera when its himself and not a puppet.
Now having said that, having a skilled puppeteer isn't as much of an attribute than most people would initially think. A film ABOUT Jim Henson and his life would be the behind-the-scenes story...we don't need to see a whole mess of scenes of him performing - some yes, but not a large amount - it's the stories of HOW these productions came to be and Jim's other roles besides that of puppeteer that would ultimately be focused on. If you had an actor that was perfect for Jim in every other way but couldn't quite get down a lot of the more advanced puppetry aspects, there's a lot of work-arounds (again keeping in mind that you don't need a lot of shots of him puppeteering), long establishing shots setting the scene, closeups up "Jim" with the puppet help up (and out of frame) looking at the monitor delivering the lines into his foamy headset, cut to a shot of the puppet (being performed by a more skilled puppeteer)...you can even do similar things in a scene depicted a talk show or public appearance where Jim and Kermit on his arm are being interviewed together - in a good medium close up shot you can actually arrange it to look like it's Kermit on "Jim's hand" but the frog is being performed by someone else (watch Inside the Labyrinth for some of those scenes with David Bowie and the person doing his juggling).
There's really a whole movie that could be done and story that could be told about his teen years to his early success with Sesame alone. Not that i'd want that to be the whole movie but one could get a lot of mileage out of those early struggles. Really considering the grand scope of his life even though he died relatively young, to tell a decent story of his life, it would have to be between 2-3 hours.
When doing a biopic, it helps if you can get someone who can be a good "lookalike" either with or without heavy makeup but some of this can be sacrificed if you find the right actor who can embody his spirit. It would be just about impossible to cast the part though without having someone very tall and skinny not just because that's a common physical atribute that people always remember about him but also because his height was a major part of his personality development, being more shy and soft-spoken, tendancy to slouch, etc. (That would eliminate me, lol, i've got the acting and puppeteering chops and knowledge of the subject matter but could never meet the physical requirements!)
I don't have any fears about the way Jim himself would be presented. Granted not knowing much about the people working on this, but any biography worth its merit on Jim would need to be more concerned about how the heck to portray him WITHOUT him seeming so goody-good when so many people who knew him constantly talk about his lack of flaws, almost near inability to get angry, constantly set an example to others about how to deal with stuff. Does that mean your script is without drama? Not in the least - just look at the guy's life story! You'd see a lot of how people around him are reacting vs how Jim is managing the situation...as well as the contrast between the show business world's more jaded ways of working and Jim's fresh approaches.
Of course this would make it all the more trickier to get Disney's involvement approval - because even more than the Henson family (and we all know how protective they are), Disney would be all the more harder to deal with - they would want not only to be credited and paid well for allowing the Muppet likeness but i can't see them not also being protective (to the point of making it a condition of granting the likenesses) of how the Disney company is portrayed - and let's face it, the Disney approach vs the Henson approach would be a much needed contrast if you're going to show that part of his life (which would be almost necessary..still could be glossed over in favor of the drama of his death, but still at a hige cheating of the project's integrity)...as necessary as it would be, you would not see a scene depicting an incident like Jim meeting with Disney execs ironing details of the acquition with Jim saying "all I want is a fair deal" and being told by a Disney CEO (don't remember off the top of my head who's attributed to the quote) "grow up, you're in Hollywood now". Again, the film can be done without that Disney conflict (keeping in mind that a film depicting his life would need to be over 2 hours as it is so this can easily be stuff that gets cut, sacrificed and/or glossed over) with only mentions of Jim's selling to Disney and instantly focusing more on the shock of his sudden and unexpecting death "pushing" the "Bad Disney" parts of this era out of the story. There doesn't need to be (and shouldn't really) any big depiction of the struggles the Henson family and company have had with Disney after his passing as the movie should end with the memorial (the big vibrant celebration and foam butterflies) fading into words on the screen giving a brief epilogue of how the family and company continued to honor his creations and visions and that Disney finally acquired the Muppets in 2004 instantly going into the credits and either something like "Bein Green" or "Rainbow Connection" playing over the credits or more music from the memorial...possibly even a recreation of Steve's debut as Kermit in the "Just One Person" number from the Muppets Celebrate Jim Henson.
I think that covers the various thoughts i had on all this - i know i'll think of a couple other things i wanted to say after i send this through.