I have been thinking of all these things. Stainless Steel was the first one to come to mind, possibly some other metal, i haven't done reasearch yet.
1) I don't see any reason wy the intonation would suck, it would be exactly the same as a regular fretless, perfect.
2) Although it won't sound fully fretted, it wont sound as dampened or as woody as a regualr fretless.
3) I want a fretless for bluesy-style playing, some thing i can slide around real fast on.
4) I haven't figured out how to attach the fingerboard to the neck yet. I was originally thinking glue, but it is now apparent I will need to possible bolt from the back, or have a 1st fret which will act as a zero fret where 2 bolts will be between it and the nut. And where the 22nd fret would go, recessed bolts, which are level with the fret board. I would never go to the 22nd fret anyways...
I could have the metal i use heat-shrunk or whatever so that it stays a common size. Also, the temp of my room does not change much, and that would be it's permanent position.