What about improving Liberty to make more possibilities for multiplayer? I'm taking not about hi-res textures or high-polygon geometry, but about fixing what Rockstar did. Like fixing collision model of Callahan bridge, adding missing roofs, create normal Stadium, fix lighthouse making it easily accessible with boat, fix collision model of cutscene rooftops. All in GTA 3 style with original textures and geometry polygon-count level. Not create something new, but fix old issues.