Of course I don't expect Kate Moss to pop out in the PV or anything, but yes, it would be interesting if she did since they both are RIMMEL models now.
I actually do think she means 50 celebrities from around the London area. If you look at the ViVi scans, in the pictures for Microphone, there are already about 20 people there...it's not hard to fit 30 more into a PV somewhere, whether it be in the background as an extra or actually in a scene with Ayu, either way they are getting paid to do it. So yea, it's really not that far fetched to say she has at least 50 celebrities/models from around London.
I agree with th, the men in the background could all be professional male models from the London area.