Originally posted by GeneV I'd add to what Rico said that whether it is possible to build such a lens is a different question from whether it is possible to build, market and sell it at a profit.
And there we get to the question of just what a target audience (prospective buyers) would want or do with something WIDE and FAST. Mid-range is something else, and a 30/1.4 is mighty damn tempting from a low-light perspective, but it bumps against the DOF issue. Y'see, part of what makes ultra-Fast Fiftys (f/1.2, f/0.95, etc) exciting is ultra-thin DOF. The DOF of a 30/1.4 is only slightly thinner than a 55/2.8, and is rather thicker than a 58/2 like the cheap Helios-44. Note that the DOF of a 50/1.2 is slightly thinner a 55/1.4, and slightly thicker than an 85/2.
[You may ask: How d'ya knoiw that DOF stuff? And my answer is, the comparative DOF index: Divide the focal length by the maximum aperture; higher quotients mean thinner DOF. Y'all can build your own spreadsheet to compute this.]
Anyway, a shorter lens means thicker DOF, and that's just how optics works. If a large chunk of a target audience wants thin DOF as well as low-light performance, they WON'T be in the market for that wide fast lens. Would a 15/2 or 14/1.4 be tricky to use? A dSLR version would certainly be huge and costly. So, how many buyers will fork-out US$5K+ for such a monster? I'll guess that the bean-counters at the glass foundries have figured it's not enough, else we'd see some around.