There will be a Black Crowes reunion, but I personally don't think they'll fit to BKS.
I have real problems to predict exciting headliner for BKS next year.
I'm still hoping Nick Cave will be announced (Ziggo Dome is sold out) and would love to see The Flaming Lips (only confirmed European show so far at the end of May), Björk (not that realistic, after not playing 2018, which would have fit much better) or The Chemical Brothers (no 2020 dates so far) headline BKS.
There are also some bands, that could headline BKS as returning bands (Portishead, The Pixies, The 1975, Noel Gallagher, Elbow,..), but I personally would prefer bands that haven’t played BKS before or have played DTRH in the last couple of years.
Other options could be the before mentioned Lana Del Rey, The Strokes, Tame Impala or a band like Kasabian, but those wouldn’t get me excited.
Sonic Youth would be amazing, but it's hard to believe that Thurston Moore and Kim Gordon will perform together again.