It seems likely they'd have to stick with f2+ for anything as small as their e-mount series. I'm OK with that, since Sony seems to be taking the opposite approach with the new 35/1.4 and 90/2.8. A range of options in size and speed would be nice.
I do wonder what they're plan is to develop FE lenses though. Sigma is a small company, so in the past they've shared lens development resources with multiple product lines. It's pretty clear that the 19 and 30 were originally created for their DP1 and DP2 cameras and added to the NEX and m4/3 lines later. But developing an FE mount would not fit with any of Sigma's existing cameras. Maybe they'll use a focal length that would be desirable on both 1.5x crop and full frame (and even 2x crop?). Maybe 24mm f2.
On another note, DPReview released their Zeiss 35/1.4 samples and they look pretty nice.