Ah, yes a new Doctor! One of the things you can count on, just as you get familiar with the Doctor, ZAP; Change, new Doctor! Used to bother me to no end when I was younger, but now it's just a part of the character.

As to coming back as a female; I donna know, might make the ingénue side sidekick part, well not so important. Sexual tension you know, might not be the same with a swashbuckling female and a mousy (not to say all the Doctor's sidekicks were mousy) male... Defiantly wouldn't work with a mousy Doctor. Although now to think of it I do remember a BW portion of the series were the Doctor and I think Jenny get their bodies switched, funny as all get out.