SIGMA is actually reworking his whole lens line. I think we should expect 2 to 4 years before having a new useful SIGMA lenses panoply. They also design new lenses such as the 18-35f1.8, wonderful lens.
For me, this is logic that they should work on a new 50f1.4 ART lens, justly to counter this self proclaimed "wunderbar" Zeiss Lens.
The actual 35f1.4 ART is a masterpiece, it is notorious. This is the best 35mm out there. It is a solid piece of metal/composite and glass. They have nothing to envies from Zeiss about that. Actually, I prefer the SIGMA over the Nikon big times in build construction. They also test and calculate it to resolve the last foveon chip, which is very hard to resolve. Also the 35mm feature a lot of elements too, this is not a simple optic.
SIGMA is on a new way and we will forget about the old design once new lenses will reach the market. Let say a 24mm, a 35mm, a 50mm, a 85mm and why not a 135mm...
There will be always a sort of apprehension from consumer PoV about buying a SIGMA lens over a NIkon or Canon lens but SIGMA will prove that it is wrong and stupid, at the end. The Price, the excellence of build quality and the excellence of optical performance. They do and can do it.
So, lets wait for the new 50f1.4 (why not a 55f1.4). Sure it will be awesome and very close (if not identical) to this zeiss in performances, + AF
Do not forget that the lenses are mostly telecentric now, in SIGMA world. They are obliged to resolve the corners of a chip who do not have micro-lenses, as far as I know.
I think SIGMA will overcome Zeiss in a not so far future, in term market/technical reality. I mean, Japan people do not joke... You might LoL at my assessment but I'm pretty serious !