[Bethwaite] now believes that thin round sections are practically better...
Umm, that's a bit of an over simplification Steve.
I just wrote (while waiting for some big photos to scan) 1100 words of reply to this which was still about half complete so perhaps I'd better find another medium for my pontifications on the subject.
Suffice to say I've got some experience playing with wing masts, I own one of Bethwaite's original wooden ones, and whilst I think that the Canoe platform would be a good one for an overrotating wing mast the sheer amount of development work required puts me off.
Arne, I would applaud and do my little to help anyone who wanted to take on a development project on this scale. I can tell you more about things that haven't worked than things that have though.
I reckon with finger in the air that you ought to reckon on building at least three complete spars, plus a lot of gluing on and sanding off of unidirectionals before you get one that really works.
I would be very wary of a pear shaped section, I think you probably want something with a finer leading edge.
I think you're on exactly the right track by seeking to separate the aerodynamic section from the mechanical section, but I would be inclined to put the fairing on the front and the structure and track at the back.