'If my Doctor had carried on he would have become a bit meaner and a bit tougher.'He then went on to say,
'The universe would have weighed on his shoulders a little more which would have been cool.'Karen Gillan then spoke up saying that if she had stayed on then the possibility of meeting her four psychiatrists (mentioned in The Eleventh Hour) could have been in contention. A fan then suggested that Matt play the companion and Karen play the Doctor - 'Inform Steven Moffat' was Smith's response before realising this may result in him playing a kissogram!
[Source: Radio Times]