Something along the lines of the Ford RS Owners Club would be good. I was a member a few years back; very well organised, good discount schemes, excellent club mag etc.
It would have to be exclusive to some degree to have any credibility; how about an international Audi 'S' Club, open to owners of all 'S' badged cars, past and present, containing registers for S2, S3, S4 and S8, with a special register for 'RS' badged Audis?
Go for it, Wando. Think of the kudos !!