The new footage is probably A Slice of Lynch part 2. I wouldn't get my hopes up apart from hoping for a kinda cool extra. I can't remember where I read it, but there will be an interview-ish deal with the Palmer family (Grace Zabriskie, Ray Wise and Sheryl Lee), which sounds cool. It's probably that. Or another deal. But David doesn't need to use this to sell an original work, not even a Twin Peaks one. I think this is an archival release with some strictly documentary extras (but I've been wrong before).
Since you bring up Wild at Heart... I'm willing to bet Wild at Heart scenes in good quality would save the movie for me. That's the one film, imo, where David Lynch fatally miscalculated how dense his script actually was, and ultimately screwed up. Cutting Blue Velvet, Inland Empire, and even FWWM worked really well and possibly even improved the end results (as much as I'm looking forward to FINALLY see these scenes!), but Wild at Heart is an almost Dune-like mess that would have been better as mini-series. (Sadly, those scenes are probably long gone.)