Yeah, I don't know what's holding him back. I was able to collect some of his collaborations through purchasing CDs from various artists (out of print, used, etc.) and a lot of that stuff is really good. It'd be awesome to have it all in one officially released collection (or a box!).
Joe Lynn Turner released something similar to that last year (albeit on one CD only) and I thought it was not bad.
I totally understand that some artists don't care to look back and all about the future, but at the same token when do you take a breath and take stock of everything you've done? Celebrate your music sort of thing...
Anyway, just my wishful thinking. But hey -- it's almost Christmas, so it's allowed