Besides the usual "I am in grad school and never have more than a few minutes to rub together," there are a couple of big roadblocks on SuperSkein right now:
* Processing's handling of threads is very itchy, and as the GUI has expanded, it's slowed down to molases-like speed, and I can't think of a way to fix this.
* The easy problems are solved, so only the really hard stuff (infill, etcetera) remains.
Revar is working on something he's calling Mandoline which now has infill, and since it's written in C++ it's VERY fast. However, no GUI. Meanwhile, SkeinForge has seen a lot of updates, although it's still not very readable and has, in my opinion, too many options still. It's nowhere near as bad as it used to be, and the default profiles are better, but that's still a big challenge.