I think just about everything that runs on a Quake3 engine uses the idmaster, that's a lot of titles and a lot of them are triple-A titles. Plus, there's the tie-in thing: id sell the game engine, support for the engine and the master server - even if their master server is losing them money, it's a loss leader because they make it back from sales of the engine.
Anyway, this seems to be a good oppertunity right now. Possibly the larger publishers would be able to provide one as part of the service package. Possibly a startup could do it, bit risky though since probably be a fair bit of capital and developers would (hopefully) have reliability as a priority. Possibly a company (or network of companies) who already has most of the infrastructure could do it - a collection of GSP's perhaps, or some webserver firm looking to diversify.
This comment was edited on Dec 9, 12:27.