I agree with you ive longed for a 24-105 f2.8L IS for ages
I'll add my
35-85 f2L IS with IQ as good as the sigma 35 f1.4
I've heard you mention that lens before, and I think it's a pretty interesting and unique idea. From a size standpoint, I believe it might be reasonable (although, since I'm not an optics engineer, I'm not sure how difficult such a lens would be to design). Sigma (with the 18-35mm f/1.8) and Olympus (with the 14-35mm f/2 and the 35-100mm f/2) have proven that zoom lenses can be designed and sold with apertures greater than f/2.8 (albeit with a smaller image circle). The lens you have proposed is probably the ideal candidate for a larger aperture zoom with a 35mm image circle (wider than 35mm or longer than 85mm would probably start to make the design prohibitively large).