Well, so far there's been reports of
Kara Tointon,
Sharon Osborne and
Richard & Judy. Kara would probably be good but I'd really rather Sharon, Richard and Judy didn't do it
Amanda Mealing, who a few people have mentioned, would probably also be good to watch.
So would Rebecca Adlington, who's also been mentioned a few times. (Didn't someone say she wanted to do it last year but didn't get back from the Olympics in time?) She was in the audience once or twice during series 6, so I'd say it's a fair guess she likes SCD.
A few people have mentioned Fern Britten and I wouldn't be at all surprised if she does it. She'd probably be good too: she was quite good on Let's Dance for Comic Relief.
Someone also mentioned Jennifer Saunders but she's never done any other reality tv show... her husband, Ade Edmonton, on the other hand, has done a couple so it wouldn't surprise me if he popped up on SCD one day.
Also, Felicity Kendall was in the audience a lot during SCD6 and was even asked to help Christine get into character one week, so I've a feeling she might do SCD7. I'd imagine she'd be as good as Cherie.
Angela Rippon's also said a few times she'd love to do it but I believe she's got a lot of dance training so I'm not sure she'd be allowed to do it.