I see it as highly unlikely for two major reasons.
 
1. The TITAN X is the flagship card at nearly double the cost of the 1080. A super flagship card like 1090 would have to be a dual TITAN X chip card*, at a very low production volume, thus high cost. If such a thing was brought to market you'd be looking at $2500 minimum (IMO). 
2. Nvidia's stance on SLI has changed with the Pascal GPUs. Except for a very niche set of benchmarks, using GTX 10 series GPUs will only allow SLI with two GPUs. That would mean a TITAN X2 (2 TX GPUs, 1 card) would be a single card solution and wouldn't support dual card Quad SLI like GTX 690's. (i.e., you would be limited to one card, there wouldn't be SLI support for two dual chip cards.)
 
*Using dual GTX 1080 GPU's would likely result in a price near enough to the Titan X to cannibalize its market share.

I would also say no for the 1090, they have not released a x90 series card since the 690 which came out back in 2012.  Also like Halo_003 mentioned it would ruin the Titan market place and there is no support or way for Quad SLI.