If the top bends, it eases gust loads
The sheeting is not specified in the Catalyst article. If it is as with a lug sail, single sheet and control twist partly by tension on the tack line and partly by how much sail is before the mast, then I can see that happening. If the plan is to use junk.rig-style sheeting, then the upper sheetlets may hold the upper leach in place while the mast bends, increasing angle of attack up top.
Combining the Wharram and Freedom wrap-around-the-mast soft wing the Slieve's split junk looks like it should produce a rig with good aerodynamics for its costs. There seem to be conflicting experiences with reefing this kind of soft wing: http://wharrambuilders.ning.com/forum/topics/wingsail-rigs-a-nightmare-in-the-rain. The join of lower to top mast may make that worse. Rob Denney (also an AYRS member) is working on a telescoping wingmast, and puts the wider tube on top. That might be worth looking into. If junk-style sheeting is used, that might help, because tightening the idle sheet should pull the whole sail forward and should ease any binding of sail on mast.
Finally, when the boat is ready, may I come sailing for a day? My current boat is too large for my liking. Once I sell it, something similar to this design (though smaller) is one option.