It would be great to mix it up and either go with one classic act, one return act and one first timer; or even do one metal, one rock and one pop-punk such as:
A7X / AC/DC / MCR
for example.
It is, however it also appears if you use Metallica and Slipknot (just a couple of examples I tried) so wouldn’t take that as confirmation. A7X however does list Download Festival on the 14th June under Events so I’d say they’re nailed on for the Friday.