I borrow my friend's 180mm OS from time to time and its a good lens as well. Apart from these two 105mm OS is heavily discounted(down to 469$) right now as if Sigma wants to clear inventory for these lenses and not making new ones.I have the 150mm macro, and it's a great lens.
Still EF mount is one constant in the whole sea of MILC mounts. I know the horrible Sigma QC(due to 150-500mm OS) but somehow the Macro lenses in general seem to have better QC. Also Sigma was the only one who offered image stabilized 180/200mm class of macro. I really hope if Sigma doesnt update their current macro for SLR mount we get MILC macros for Rf mount.Everyone is affected by slowing camera and lens sales. The companies also have to deal with the deluge of mirrorless bodies expected to flood the market. Its sad, but a buyer can get hit with a recent lens that can't get support or repair after just a few years. It happened to me with Sigma which is why I avoid them.
True, also since its going to be dedicated macro wouldnt mind if Sigma were to make it f4 to save on weight. That old 180mm f2.8 is quite heavy lens to lug around in field.180 Art, RF mount would get me to buy a R or RP. Unless it has the fiddly focus-by-wire that the 70mm Art has.