I think the bigger issue you all seem to be missing here is that The Doctor will be regenerating at all!
It was clearly established in the first serial that he was just some old dude that lived in a scrapyard. Non-canonical elements like him being a Timelord and being able to regenerate, were only introduced to explain away the change of actor after 5-years. The canon should be respected and all episodes after Hartnell should be erased (something the BBC tried hard to do back in the day!).
If I am not mistaken the very first episode makes clear that the Doctor and Susan are not human. No, regeneration was never explained until 3 years later, but I don’t see how regeneration violates the cannon.