I certainly do feel that games designed and that can only be played by a certain age demographic would succeed. While the majority of ROBLOX players are under the age of 13, there are many older players who would enjoy games that emphasise on adult themes unlike the cartoonish aesthetic in games designed specifically for enjoyment by a community in which children are the majority.
But then again, games designed for adults tend to be enjoyed by children as well (at least, some of them). I played Call of Duty and Battlefield before I even hit the double digits and I enjoyed it much more than any other game I had played until then.
However, there is a difference between mature and plain horrible. I wouldn’t want games on ROBLOX with the same themes as games such as ManHunt or Postal.
Games that explore darker themes and excessive levels of violence that are designed using the ROBLOX engine will probably never be allowed, let alone played. However, I’m all for games that are designed for a mature audience, as long as it isn’t excessive.