Like many artists focusing on their own shows, it is not even clear Nick Cave will do a festival tour on this iteration. In fact, the lack of any announcements so far suggest he might tour Australia/Asia and then that's it. I know there is a festival date in Los Angeles, but as headliner and as a one-off during the regular NA tour. He probably likes the money of a festival run, but I'm not sure he needs the exposure or the scheduling trouble with band members also playing in bands such as Radiohead, The Smile and Dirty Three! I mean he is probably at the opposite end of someone like Lana Del Rey who thought she deserves a main stage slot (maybe with good reasons, but that's not the point here).
Coachella had one bad year. They are clearly struggling right now with which direction to take. Plus it’s getting ridiculously expensive. But if they started to book bands like RHCP, I don’t think their ticket sales would get better. Their target audience is just not interested in that. Blur were great example this year.
Btw, you said you wanted Billie. Is (was) she also inexperienced? I mean she was even younger than Olivia when she headlined Glastonbury or Coachella…
Turnstile are a Primavera Porto which is the same weekend as Download/Outbreak. If they're doing both the London and Manchester date of Outbreak (which looks likely) then they're 100% ruled out for Download.
I will Arctic Monkeys probably had the biggest leep I'd seen from a band. The Killers as well in my mind. Two bands to do it at the time off of absolutely banger albums.