Next announcement in a couple of weeks on April 2nd (confirmed on mailing list). Thursday headliner and more bands. Maybe ASIWYFA playing another album in full. Opeth are playing Damnation so I guess that rules them out. Loads of people shouting for Mogwai but I guess you'd get that at any post rock festival. Maybe leaning too much into the metal side again but maybe Deftones (speculation based on event poll) or Gojira (short UK tour before the fest, but nothing in the south west)? Also Mastodon did a surprise UK tour at the start of the year, maybe they'll come and do Crack the Skye in full.
Although most likely I'm being full of myself, none of the bands will be so big but I'm sure they'll be awesome.