Yes. There are tons of open, difficult rationality/philosophical problems. If they haven't 'cropped up in a while' on LW, it's because those who are thinking about them aren't taking the time to write about them. That's quite understandable because writing takes a lot of time.

However, I tend to think that there are enough very smart rationalists on LW that if we can cogently bring everybody up to the cutting edge and then explain what the open problems are, progress will be made.

That's really where I'm going with my metaethics sequence. I don't have the hard problems of metaethics solved; only the easy ones. I'm hoping that bringing everybody up to the cutting edge and explaining what the open problems are will launch discussions that lead to incremental progress.