I am not a rationalist. Well, I am not a rationalist as the term applies in this community. Not completely anyway...

But I am here because of that Optimal Future I have mentioned.

The rationalist part is important. I agree that it would help to have collaborating memescapes but if these memescapes are not updating with new evidence then it is worthless. Lesswrong is already a community of rationalist that wants to identify and rid themselves of junk memes. Lesswrong is already concerned with non bleak futures and has active discussion with wide ranging implications for the far future, such as problems of philosophy, machine ethics, and decision theory. The rationalist part is important because it already implies we care about FAI, and optimal futures. It's not worth anything to know what a Friendly AGI would look like if designed by an anarchist, if that anarchist isn't also an aspiring rationalist, but rather seeking an anarchist future for the sake of an anarchist future. If you look at the topics of discussion you will already find the gamut of different memescapes that you referred to. Assume optimalfuture.org takes off, if you start to prune the junk from all competing futurist ideas you would start to converge to the most "less wrong" ideas, basically you just end up with LW.

I may be wrong and may update on it later, so I'm not completely dismissive of the idea. I book marked the site and will check it from time to time because there could interesting discussions.