I'm trying to find the original interview, but I do remember one of the Sigma executives saying that the E-Mount is a difficult mount to make lenses for. (This could explain why there's so much in-camera corrections.)
That being said, they have since said they will make E-mount lenses.
It's difficult to make dedicated, more compact lenses that take advantage of E-mount's shorter flange distance, particularly for UWAs (you still need a retrofocus design to reduce the angle of incidence of light hitting the sensor)
It's ridiculously easy to make an ordinary SLR lens perform just as well on an E-mount, if you're not also trying to make it smaller. It essentially consists of taking off the SLR mount and replacing it with a Metabones adapter, inbuilt/permanently bolted to the lens.