Hello.

*[i]assures everyone that I have years of experience on RP sites and am subsequently qualified to interject[/i]*

As a previous GM who ran a simple open-world RPG, with theoretically infinite options based on player choices, and as a gave dev who tried making a game based on that RPG, I have found that, invariable, players need some kind of plot or story to fall back on. Stick a bunch of kids in a magic sandbox with some toys and buckets, and they'll have fun for a while, but eventually run out of things to do. Even Minecraft, the undisputed king of free-for-all sandbox gameplay, has objectives, achievements, and an "End," so when you get tired of building a space tower out of cobblestone you have something [i]worth doing.[/i]

If you're going to have an Expanded Universe, I stress that it have a start point, end point, and a line that leads between the two, so when the Dragonborn gets tired of setting people on fire and stealing cheese wheels, he has something to do that [i]makes progress,[/i] even if it just means a new city to steal wheels of cheese from. The line can be a thick, thin, wavy, or convoluted as you want, as long as the RPers have something to, well...you get the point.