Oh please... Have pity on an American Whovian and tell me... Once C. Baker was on board, had they planned to do it AGAIN?
No it is to do with Robert Holmes's original story which had the First Doctor being replaced by a robot duplicate.
Excepts from the original version of "The Five Doctors" exist in a copy of a booklet published in honor of the anniversary called, "The Making of the Five Doctors" and it was put out by either the BBC or the Dr. Who Fan Club of America...I don't remember which. The artwork on the cover is awesome and the title of the booklet is embossed in silver. I've still got a copy of it somewhere....
And in keeping with the tradition of robot duplicates of the 1st Doctor, this one was distinguishable because he: 1. Actually remembered his lines. 2. Moved his lips completely independently of any words coming out. 3. Didn't look a thing like the Doctor!!!!!