This is a neato idea! I'm curious how this would actually function within the game, but what you're describing is pretty cool :)
I like the idea of an advertisement channel, I'd like to believe that even simply renaming "General" chat to "Adverts" would significantly reduce the amount of spam. And with our shiny new team of staff, regulation would be easier. Then there's always the option of turning off that specific chat, though those looking for a roleplay may become...irritated with spam. However, spam is something nobody can escape from, where there is a chat there is spam. So of course where there are varying chat channels, there will be spam haha
I think a trial run of something like this could be beneficial, if just to try it out and see how it goes!