Restrictions will lift I think by then but gatherings of this size will still be off. I reckon even late festivals will go. Kendal Calling have already gone for softening the blow before they have to confirm it.
Just be responsible folks. Forget about missing a festival. I decided a couple of weeks ago not to go to Ash and I'm keeping the ticket, because I don't want others putting people at risk. It's not worth the risk.