Still don't care for the change to blue (circle or otherwise). Would rather just see a thin, lighter border added to the original S to give it more contrast.
I can't begin to tell you how little I care about corporate users who gravitate toward slick-looking proprietary software.
And yes, different icons could be used for different platforms. I, however, would not be in favor of dividing the Sigil brand across the various OSs. The shapes could vary a little, but I'd prefer a general continuity myself.
I'm voting "no" on this one. Not because I'm opposed to change (or wish it to be "left alone"), but because I don't care for THIS change. But as I said, I won't stand in the way if there's overwhelming support for it.