I am surprised though at the seeming lack of activity of interest in this area

I'm highly interested from a professional standpoint, it's a fascinating problem with lots of cool graph-theory type implications and room for all sorts of whiz-bang algorithmic voodoo. It's great. But as far as email goes, I'm *already* super organized, so I don't need the app at all. This is part of the problem, I guess, because someone who gets to the level where they can appreciate something like this probably doesn't need it, or could otherwise write similar software. But again, the theory is highly fascinating, and I'd love it if more things worked as an intelligent (emphasis on intelligent) database rather than a hierarchial file cabinet.