Better dynamic hair would probably be first on my list. (Including shaders that look good in Superfly, though I guess that might take forever to render.)

I love Tiny's furry cats, but I know it took him a lot of work to set them up. I don't know why, but dynamic hair tends to have "strays" that ruin the render. Tiny tried to explain what the problem is -- something about strands at the edges of polygons or something -- but I've never been able to fix it myself, except with postwork.