I was thinking along similar lines. It makes absolutely no sense. The music isn't as good as the solo work by Robin Trower who unashamedly copied the style of Hendrix. It seems a bit like when there's an ad on TV where they couldn't afford to use the real song so they paid someone to compose something that sounds quite like it (but not enough like it to infringe copyright). Perhaps the studio thinks there'll be enough fans of Andre 3000 / Outkast to go and see it but, as you allude to, I can't really see anyone wanting to go and see it if they aren't into Hendrix and, if they are, they're going to be disappointed.That's really weird that they would go ahead with a production like that without having first secured music rights. The music in the trailer is really off-putting and generic (to a guitar player - but who else would go see it?). It stuck out right away as being inauthentic, so I'm not sure the movie is exactly destined for greatness.
Having said that, they made Good ol' Freda with only four Beatles songs. But of course that's four more than this Hendrix thing has. Doesn't mean I won't watch it, but I won't be paying to see it in a theater.