Dxomark.com now has tested the 5DS so you can compare it to other new cameras now. While the 5DS cameras have very slightly (.7 EV) higher dynamic range than the 5DMkIII and very slightly better low-light performance both the Nikon 810 and Sony A7R have significantly better dynamic range (2+ EV) than the 5DS. It seems to me if you are a real estate photographer there's not much point in upgrading to the 5DS. Just more pixels is not much of a motivation for a real estate shooting.
A better alternative, if you are searching for more dynamic range and low-light performance would be to go with the Sony A7R and adapting your Canon glass to it with the Metabones Canon EF Lens to Sony NEX Camera Lens Mount Adapter. If you are a Nikon shooter you could use a Metabones Nikon Lens to Sony NEX Lens Mount Adapter. And you get all the other benefits of mirrorless as well. It appears that the ability to use non-Sony lenses is a big help for Sony to get photographers to switch to their full frame mirrorless line.
Any mention of the Sony A7R at would be incomplete without pointing out that there's a new Sony A7RII about to be released (expected Aug 10), but this new Sony will be $1500+ more than the A7R.