There is perhaps one positive thing about the ending with the Doctor's other half remaining with Rose. If the BBC ever want to do a multiple Doctor / companion adventure in the future, Tennant and Piper will always be able to do it, however old they are.

Just imagine Tom Baker trying to come back to Who nowadays. He's changed so much it just couldn't happen (though BabelColour can help you dream:

http://www.youtube.com/watch?v=4knUJKUNbqI ).