Is there a point for a 30/1.4?
If so, why no point for a 18-35 which is only 2/3rd of a stop slower? Its basically a whole bunch of primes in one lens as far as aperture goes, which means you get the convenience of a zoom, without the downside of slower aperture. Also, I highly doubt this lens will compromise too much in terms of IQ, since there is little point in Sigma investing in a lens that would not sell, and is probably the reason why it is only an 18-35, not a 15-40 or whatever.
Either way, this is all speculation until we get reviews.
It just seems like an odd range of focal lengths to me since it's APS-c only. But, what do I know, people may indeed have a use for this. Admittedly, I could just be skeptical since it's the first <2.8 zoom. I should probably keep my speculations under wraps until we see some reviews.