Your points are important ones. As for the gearing, that fact that this is being paired with an IGH is important. The Sturmey 8 IGH starts out at 1:1 as its lowest gear and steps up from there. It has a double-size step from first to second and 7th to 8th, resulting in a hi/7th gear of 90GI, and a hi/8th gear of 117GI. For a very strong rider, the rear cog on the Sturmey can be changed down a few teeth (they make a 22 or 23 tooth available). But those high gears are plenty for me! I will concede the double size step at the top of my range is not my favorite design nuance of the Sturmey.
As for the longevity, you are right that it is basically untested. In making my decision to take the plunge, I was swayed by the facts that a.) it has a respected company behind it, so they must feel like it has merit, and b.) it's actually about the same price as other decent, but not top-shelf, cranksets.
So I'm one of the guinea pigs. Of course I'm not an especially strong rider, I don't ride a lot of miles, and I don't ride in rain or snow, and my bike is always stored indoors in an environmentally controlled area...but other than that I'll use the heck out of it!!!