Nice idea, but I think too many of the winners have moved on to other things in their careers (and so have some of their pros) so I'm not sure who they'd get to do it.
I don't think Natasha, Jill, Alesha, Tom, Kara or Harry would do it. Some of the others maybe, but they'd probably have more success getting runners up like Rachel Stevens, who always seems to be available for a special.
Even if they did do it, I think it would be a bit weird to see them with different pros and would probably tarnish the memory of their win if they then went out first in an all-star series or were just a bit more rubbish than everyone remembered.