Pardon my late response, I pulled a late-nighter last night and just woke up.
I understand what you are getting at, Vaereir & Neail, and I agree, to a certain point. If you are roleplaying constantly, then there isn't any use for a Roleplaying Mode, I agree. But you're not necessarily roleplaying when playing a game. When you play a Troll in WoW, you're not roleplaying a Troll by just playing that Troll. That Troll is an avatar of you, it'll will talk like you(Because it is you :p), and behave like you. When you roleplay that Troll, you'll talk like it, give it a personality and likely interact with the world.
I understand that a VR is going to be very different from the medias that exist today, and you can pretend to be a completely different person if you'd like, and that would indeed be roleplaying. But I doubt that everyone would be like that, because frankly, that could prove tiresome for some, and I'd imagine that people would want to talk about everyday things, like the latest update, hackers, real life news and what not.
I've roleplayed for many years, and I've encountered many different forms of roleplaying. And one of the most common forms of roleplaying is so-called casual roleplaying, where you go in-character on the whim, and interact with other characters. When you're tired of roleplaying, and want to hang out with friends or train, you go out-of-character.
Another common form is that guilds and clans will form player-owned-kingdoms and cities(PoKs & PoCs respectively), forming a new environment. People will interact with said kingdoms and have specific roles, such as being the king, a guardsman, a smithy, a court jester and what not. Eventually, other groups will start to pop up, such as cults, churches, mercenaries, bandits, noble families and plots.
World of Warcraft, RuneScape, Guild Wars 2, Star Wars: The old Republic, Minecraft, Garrys Mod, Rust, Mount & Blade, countless forums, they all have that, and SAO will be no exception.
But that's just my experience with roleplaying, and I thought that RPM would aid people with detecting other roleplayers and current roleplaying sessions. Also, muting people was only added as an afterthought to the potential trolls, personally, I wouldn't mind that, but neither would I think that it is vital to have.
Last note, excuse me if I didn't make myself clear in this post, I was a bit fuzzy when writing it. :s
In any case, I appreciate the feedback! The more the merrier!