A thought I had about dedicating an FM room to different things

It's a good idea, but getting the word out would be difficult. Unless Nexon endorsed it and advertised it to the general maple public, it'd be difficult.
Also, I doubt most people specialize in one thing. Most people have a mixture of scrolls and you'd need to buy a ton of mush shops to be able to put them up around.
In theory, with multiple stores, yes. In practicality, not so much.