I very much enjoyed Francisco's original corsair 150D idea.
something along the lines of this:
In the roof, it would have the same capacities as the 350D in the sense of 240/280mm rad support. One bay would be completely sacrificed for the 280 option. That leaves the lower bay open for people who still use the bays. However in the front it would only have 120/140mm. At most a slim 140mm rad with one push or pull fan after the cage is removed.
Now, i understand that this ''150D'' is only marginally smaller than the 350D but, I'm from the point of view where SFF and m-itx can be thought of as separate things. On one hand SFF is trying to fit as much performance into the smallest volume possible. Whereas m-itx would be considered to be the smallest layout in which maximum performance can be achieved (with 1 cpu, 1 gpu and atx psu on an m-itx board), in which this 150D fits.
On the subject of it being an obsidian line case, i think it fits the theme of the lineup. It can be packed full of performance, has the support for ample water-cooling and maintains the obsidian lineup's sleek and refined looks.
In the end, this far into it, I can only assume that Corsair most likely has a design already selected. At this point, we may only be speculating what it could be. That said, we can dream cant we?