I've been contemplating the idea of making a Cats cast database... it's a daunting job tho!
We've done similar over on the Starlight Express Wiki - where every cast member has an individual page. These range from the most basic, such as Anna Woodside (Current Demeter in the Palladium) to a full career page with photos, interviews and links like Mykal Rand (18 years on skates as well as working as resident director).
Part of what I find very interesting is when people have started as small roles in one production, then moved to larger roles/into directing or choreography, and that earlier experience influences their work later. It's also interesting to see who worked with who in the same cast - for example, Ruthie Henshall was Jemima to Anna-Jane Casey's Rumpleteaser!
Starlight Express is a much smaller show - as in, there's been 10 professional productions world-wide, and while the German show is in its 28th year now, there's detailed archives. We've managed to assemble a nearly complete database for Starlight, but I don't think it's possible for Cats. So often we only have a list of names, not the roles they played. However, I think it'd be worth having an interactive database, each actor having their own page detailing where and when they were in the show, and with photos wherever possible.
So, the question is - is it worth setting up at least a partial database? The format here means anyone - including the actors themselves - can access and add to the information. Anyone with a playbill can add to the database. Also there's a sense of aknowledging and respecting all the amazing performers who've been Cats over the years!