I think trying to make a sequel to something like Gmod isn't going to work because nobody wants to abandon all the stuff they made to move to the new thing that has NONE of that, even if the features are better.
The ONLY game I can think of that did it well was LittleBigPlanet 2 (and maybe 3?) which brought over ALL of the user created levels from the first game so it was just a straight upgrade.
