OK, presumably Moffat is already planning series 5 and will not want to radically alter the existing format yet. However once the audience is used to a new Doctor & production team, I think it is essential that he experiments with something new. Audiences get bored.
My idea would be for a whole season which is one story - Trial of a Time Lord style - but that this story be one long historical epic. I suggest the Wars of the Roses which is full of drama, romance and shifting allegiances.
I'd do it in 13 parts:
Episode 1: 1450-53. Reign of Henry VI. Loss of the 100 Years War. Quarrels with Richard Duke of York.
Episode 2: 1453-54: Henry goes insane. Richard's quarrels with Margaret of Anjou.
Episode 3: 1454-55: Wars begin: the Battle of St Albans. Death of Somerset.
Episode 4: 1455-59: Isolation of Richard of York. Role of the Nevilles & Warwick the Kingmaker. The Parliament of Devils.
Episode 5: 1459-61: Battle of Wakefield. Death of Richard. Edward iV's victory at Towton.
Episode 6: 1461-70: First reign of Edward IV; Woodville marriage & alienation of Warwick. Warwick's rebellion.
Episode 7: 1470-71: Battles of Barnet & Tewkesbury. Murder of Henry VI in the Tower.
Episode 8: 1471-83: Second reign of Edward IV: Clarence's treachery & execution.
Episode 9: 1483: Death of Edward IV: Role of Richard of Gloucester : usurpation of the Princes.
Episode 10: 1483: Episode devoted to the Doctor trying to save the Princes in the Tower.
Episode 11: 1483-84: Buckingham's rebellion against Richard III
Episode 12: 1484-85: Role of Henry Tudor - planned invasion preparations.
Episode 13: 1485: Battle of Bosworth 22 August 1485. Tudor victory.