@Jens_Rasmussen it's basically just playing an rpg except there is a chat room and you can see people. At least, for now. There are mmo systems for older rpg makers too that had stuff like active battles, trading, the works (like rmx-os).
But I mean let's be real. Runescape was made with Java in like 2002. I'm pretty sure someone could make a decent mmo in rpg maker if they wanted to. At this point, RPG Maker itself is just a suite of assets and a GUI that helps you make a game. You can rip out any code from it and replace it with whatever else you want, provided it is JS.
@Jens_Rasmussen pixel/analog movement, active battle system, basic 3D, lighting, character customization, all of that is already possible with rpg maker. Relatively easily too. One could definitely make a more old-school mmo with it. There are better ways to go about doing such a thing, but rpg maker is very easy and very well designed, which is why you get a lot of slop from it but also some really notable stuff.