Well Cattail, there is a very good reason for making the neck and the fretboard from two different pieces of wood.

One of the main functions of the fingerboard is to resist wear from the abrasion of the strings, and historically, the timbers which do this best are ebony and rosewood. Those timbers are also the most expensive to purchase, and to use ebony or rosewood to construct a whole neck would be horrendously expensive, not to say a needless diminution of a valuable resource.

There is also the question of ease of working. The hard wearing qualities of ebony which makes it so suitable for fretboards renders it unsuitable for necks simply because it is so laborious to cut and shape, and is also murder on the tools. Honduras mahogany is a much easier and more suitable option.

That said, if anybody ever did make a one piece neck/fingerboard out of ebony, my guess would be that it would not require a truss-rod, and that it would never deform under normal string tension. Many of the best hand builders do actually construct their instruments without adjustable truss rods (as indeed Martin used to do) and if the instrument is built with close attention to tolerances, there is no need for an adjustable rod. There will, however always be a need for some kind of reinforcement in a guitar neck (unless of course it is made from solid ebony !!)

Murray