Honestly, I don't think this is really for the Build topic anyway - it's more demographics (what is needed? what is over-saturated?) concept than a build at this point.
That said, I wouldn't worry too much about what classes are/n't well represented. It'd be pretty hard to track because people often have multiple characters with varying degrees of play time dedicated to them. I'd say go with what you really want to play first, then from there you can get some first hand observation of the "climate" and decide for yourself where and what you want to play to help bolster an idea or group, or whatnot.

I dig the concept you've put forward. There's a lot of Holmesing about to be bad, and mages (wizards in particular, with their versatility of spells) are perfect for that, I think.