Films have already been made. Gus Van Sant (Good Will Hunting, Milk) directed Last Days, which chronicled the final days of Cobain's life. It's an artistic, intimate portrait of grief and isolation. I hesitate to put words into Kurt Cobain's mouth, but I believe the man who wrote "Something in the Way" and "All Apologies" would have adored Van Sant's melancholy film.
There was also Kurt Cobain: About a Son, a documentary featuring audio of interviews between Cobain and journalist/musician Michael Azerrad. For, I believe, legal reasons, this docu did not feature any Nirvana songs; however, it did include music by Ben Gibbard, Creedence Clearwater Revival, Iggy Pop, Melvins, Queen, and R.E.M.
As for the upcoming feature film based on Cobain's life and career, I have high hopes for it. It is to be directed by Oren Moverman, who directed The Messenger, for which Woody Harrelson was recently Oscar nominated. Moverman is very talented. He knows how beloved and legendary Cobain is. He knows he left behind a daughter. The film isn't going to be tasteless or exploitative. It will be a tribute, the way Ray paid tribute to Ray Charles or Walk the Line to Johnny Cash.
My recommendation to you: don't see a film as a "product." Direct your anger towards, say, the video game featuring Kurt as a playable character. Film is not toothpaste or a Nike commercial; film is a beautiful, unique medium which can only introduce more people to Kurt Cobain, his music, his views, and his life.