I know the discussion was originally framed to specify wood-bodied acoustics, but one option outside this is a Rainsong carbon fibre guitar. The neck on mine is uncannily like a classic Gibson ES335, and plays very easily indeed. The action is set as a normal acoustic to give a decent break-over angle at the bridge, but the neck profile makes playing more comfortable than most acoustics I've played (and that's a lot!) The inherent strength and stability of carbon fibre necks allow a very thin construction, with virtually any profile possible. No truss rod is needed, with a consequent weight saving as well.
I'd also endorse the idea of laminated necks; Lowdens have a five piece neck, which works both sonically and aesthetically. I've played some Lowdens with wideish but very flat necks, and these were very comfortable for me (I also have big palms and stubby fingers).
Mandolins are different beasts, but my Rigel has a three piece neck, a maple-ebony-maple laminate, and this seems very stable indeed.
In terms of playability, neck size is only one factor; I tend to think that action, and particularly the setting of the nut slots is more influential in determining whether a guitar 'feels right'. Just my two penn'orth.
Tim