Reading used to always have a "Metal Day" on a Sunday until a few years ago when it got traded for a more American emo/pop punk kinda day. If anything it needs to go back to how it was a few years ago and a day like that which you mentioned with the suggested bands for a Sunday again would be great.
From what I've heard, there won't be a return to a "metal day" for several reasons. Firstly, it doesn't really go with the rest of the festival, and secondly, the emergence of Sonisphere and Hevy, alongside Download, mean that metal festivals are pretty well covered.
Obvious acts are TDCC, Twin Atlantic, Lower Than Atlantis, Deaf Havana, The Vaccines, Jake Bugg and Florence And The Machine. I would expect most, if not all, to be on the bill this year.
Biffy Clyro will probably headline one day.