Well here's the trailer:
http://www.youtube.com/watch?v=1pbjo8lm1J4
I think Elvis would have done allright, and the character suited him: the self destructive 70's rock star, that once has been the most... but it was really not the kind of picture that would have raised him from his 60's hollywood standars, but just a 70's upgrade of the old musicals 60's formula, and as I said, the movie haven't aged well, it doesn't resonate well this days. So it wasn't even an improvement from Jaihouse Rock which is for sure a superior pic than A Star is Born, and it does has achieved an iconic status.
I guess the thing is that by '75 Elvis was going nowhere, so anything could have been considered a departure, and that movie being a massive hit at the box office, well, that could have leaded to other things in theory right? but well, we also know that Blue Hawaii didn't leaded to anythig better or different so...
I think The New Gladiators project, the martial arts documentals, could have leaded to more exciting things even if it didn't seem to be going for a huge succes, but at least it was Elvis's brain child, so that could have been a real departure for his artistic emancipation from then on, which in the end its what Elvis most needed, not somebody with new great ideas, but to be able to get them going on his own, with no fears of somebody stoping him, or the fear of not been liked by his audience.