Are the sources for jabo's plugins released because if someone decided to improve it, the textures could look a lot nicer (2xsai or hq2x). Also since the compatiblity works good with a lot graphics cards, it would impress a lot of people.
Jabo will release stuff when it's ready. There might be a tiny update of Jabo's D3D in the far future, and for the notes: Jabo has NEVER released any of the source codes of one of his plugins.
You'd notice mention of a version which had these things implemented. However it seems that it isn't intended for release (at the moment anyways) and is just a now and again hobby for Jabo.
So whilst from that interview it doesn't seem to be 100% dead, I shan't hold my breath for a new release for the moment.
Yep, Jabo is indeed a very busy guy and doesn't have a lot of time right now to work on a lot of projects, especially one as tough as an N64 GPU plugin (as the current bug threads for Direct64 and Rice's Video show, it's a tough job). His plugin is excellent already, but JNes could use a bit of polish