[UPDATE: The lens indeed launched. It turns out the price is $799, $100 cheaper than anticipated based on the Japanese price. Additional features now known: it has a declickable aperture ring; weighs a pound and a half (much more substantial than the 70mm Macro); and will take a 62mm filter, which is half a centimeter less than typical widths of lenses at this focal length.]
Availability is as yet unknown.
Sony E-mount shooters will finally have a roughly-100mm Macro to rival that of the old EF-mount 100mm L IS Macro. The 105mm F/2.8 DG DN Macro will launch at just below $800. The lens will also come in L-mount.
The previous mirrorless-oriented macro put out by Sigma, the 70mm F/2.8 DG Macro Art, was achingly sharp, but suffered from halting autofocus, as do most third party macro lenses. Macro autofocus is generally much harder to accomplish, especially with any speed. Shooters of many different camera brands have adapted the Canon 100mm L IS Macro after good AF-capable adapters came on the market because it was one of a few with the ability.
The lens appears to go up to f/22, which is not a very narrow minimum aperture for a macro lens. The Canon, for instance, will stop down to f/32.
Leaked pictures of the new 105mm offering show that it has at least two sets of barrel-mounted controls, presumably a set of focus limiters and autofocus controls. Not visible yet are image stabilization (OS in Sigma parlance) controls, although these are less important for true macro work. They do come in handy when the macro lenses are used for portraiture, as the focal lengths tend to make them useful for the purpose. Now that Canon’s mirrorless system has added in-body image stabilization (IBIS), all significant mirrorless manufacturers are including the technology, and that feature in lenses may have become a lower priority.
The macro market has been flooded with new options in the past two years as companies like Irix, and – particularly – Laowa/Venus have come out with previously-unheard-of lens designs, ranging from super wide angle macros to super macros to underwater probe macros… so long as you can manually focus.