People often ask this, but tend to be shouted down by fans who disapprove of recasting old Doctors. The people at Big Finish tend to agree that it's not a good idea.
At the risk of sounding childish, they did allow Jon Culshaw to portray the Fourth Doctor (albeit briefly). And the TV series itself did recast the First Doctor for "The Five Doctors". Maiku Wotaharu 01:03, June 28, 2011 (UTC)
As I recall, neither recasting was very well received, which may be why recasting isn't now regarded as a good idea. Whether or not it would work with David Troughton would depend not only on his sound but also on his portrayal of the Doctor -- convincingly giving him the same personality.
I appreciate you taking the time to answer my question. I really hope David gets to do at least one new story in that role. Maiku Wotaharu 16:44, June 28, 2011 (UTC)