Doctor Who Archive it was possible that 9th Doctor Christopher Eccleston would have been in the anniversary special but that his request to have Joe Ahearne (Dalek, Father's Day) direct was rejected by producer Steven Moffat.
Eccleston did say at a recent BFI event -
“Joe Ahearne directed five of the thirteen episodes of the first series. He understood the tone the show needed completely – strong, bold, pacy visuals coupled with wit, warmth and a twinkle in the performances, missus. If Joe agrees to direct the 100th anniversary special, I will bring my Sonic and a stair-lift and – providing the Daleks don’t bring theirs”
Interesting if this is true....