Going by the last few years..........
Couple of former sports stars - would like to see Tim Henman take this up; possibly Clare Balding could do it, maybe someone like Jonathan Edwards.
Eastenders stars - would be brilliant to see Babs Windsor now she is leaving but as she wants to spend more time with her husband don't see it - maybe Charlie Clements (Bradley) would fit this role.
BBC Breakfast star - there often is one - maybe Sian Williams turn?
Ex-wife/girlfriend of a notorious male celeb (like Penny and Jo) - so not a well-known person. Maybe Lise Mayer - partner of Angus Deayton? She fits into the obscureness but also is a TV writer.
Former popstars - am thinking maybe Faye Tozer from Steps, or an old S Club Junior, maybe Aaron Renfree or Calvin Goldspink - be something for the teenies.
Celebrities representing older generations could be Amanda Barrie (although she walked out of Hell's Kitchen), and Peter Davidson (BBC would like it that he was an ex-Doctor.
TV presenters such as Nick Knowles have always been an obvious choice who haven't done it, maybe even Gaby Roslin, a former BBC favourite.
Maybe DJ and kids favourite Reggie Yates could appear on it, and for comedy, comedian Gina Yashere.