Seems to me that Adam is already taking the Jared Leto route -- a cameo on PLL, a feature role on Glee. I really doubt that he would be consider for a lead in a major Hollywood production at this point in his career. Plus, I do not believe that this Elvis film could) get funded without a major star attached to it.
But just assuming that this fan-tasy is possible -- Adam does look like Elvis and he has something like Elvis' presence on stage. He could certainly sing the songs. And a Baz Lurhman version of Elvis' life would probably not be a literal recreation of the story.
The market - it depends on how good the movie is -- if it is like
The Doors (an inaccurate muddle of fictionalized and real event IMO, Rolling Stone liked it), it will probably not have a market and lose money.
If it is an excellent film based on Elvis' life and gets to the core of his complex story, like
Ray and
Walk the Line, it will find an audience and make money.
>> There has not been an Elvis biopic movie yet. There was a TV Movie in 1979, a dreadful TV series that lasted 10 episodes before being cancelled then the 12 episodes were turned into a TV mini-series from 1990 (Michael St. Gerard as Elvis Presley), and a TV Mini-Series in 2005 (Jonathan Rhys Meyers played Elvis).
Regarding the Elvis TV mini-series starring Jonathan Rhys Meyers -- he was good and deserved to win the Golden Globe for Best Actor – Miniseries or Television Film, the mini-series was not so good -- IMO yet another sanitized version of the Elvis story. It was made in conjunction with the Elvis Presley Estate so some parts of Elvis reality are missing.
***
There have been a few attempts to make an unauthorized (that is uncensored) Elvis movie. This project seems like it has a good shot of happening -- partly because Warners has the right to the music. They actually got the music rights intending to make the billionaire producer Steve Bing-funded biopic about Elvis Presley which was going to be based on
Last Train to Memphis -- a traditional biopic -- but as of Feb 2015 the Warner 2000 project is the Baz Lurhman Elvis film.