But Cyclops already died in X3. At least there's a reason why Magneto and Professor X can still come back. At the end of X3, Magneto is still alive and it looked like his powers were starting to return, even he's still powerless, he's still Magneto. Professor X's mind went to a different body. Bringing back all the major characters that were already killed or depowered is just too much. They are putting so many characters, it sounds exciting right now but I'm afraid, this is gonna be one of the major criticisms when the movie is out.
The returning characters that should appear in DOFP:
Future X-Men: Professor X, Magneto, Wolverine, Storm and small cameos from Rogue, Iceman, Colossus and Angel
60s X-Men: Professor X, Magneto, Mystique, Havok, Banshee, Beast, Emma Frost
Thats already 11 (without counting the cameos I listed). And of course there will be new characters. They should be careful on picking who should return.