In theory, yes. In practice, it's not presently feasible (for here).
While there might be issues running 8 GPU's (boards, case, PSU, cooling), especially on some OS's & while 7 might be more practicable, in theory up to ~16 GPU's are possible, but that's not the real issue. The last dual 'GeForce' GPU of note was a GeForce GTX Titan Z (GK110) [375W], from the GeForce 700 series. As the 1080 can theoretically do as much SP work using 180W, you're not likely to opt for a two generation old GK110 for this project. Other issues include high-end/high-cost system requirements and there are multi-GPU scaling issues. Even with 40 PCIE lanes, high end systems struggle to support 4 high end GPU's.
There isn't a dual Quadro or Tesla Pascal and for a dual socket Xeon that could support 8 GPU's you would be getting into the tens of thousands of dollars anyway.
In a few months time all this might change. High end systems will hopefully better support high end discrete GPU's and we might see additions to the Pascal range; a dual Pascal @ 300 to 375W TDP looks very doable to me and would make a lot of sense, albeit with a dollop of wishful thinking. In reality it would be at least as likely to arrive in a Titan as a GF, and neither could turn up. However, we saw app scaling issues with the 980 and it's blatantly there with the 1080, so a single GPU 1080Ti probably wouldn't scale at all well for here so a dual GPU option would make a lot more sense for the app and in terms of performance/Watt (which is alas more important to crunchers than gamers).
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