I think that you are looking at the SSG as the only possible solution.  While the on card storage is a novel idea, I believe that nVidia can compete with this in systems with GPUs paired up with PCIe x8 and PCIe x16 SSDs which have been recently starting to appear.  Also, NVLink is nVidia technology for getting more information to the GPU, so I doubt they would scuttle this effort by using on-card storage.  There are multiple ways to skin a cat, and if/when 10 GB/s workflows become more common, I am sure that all of the major hardware vendors will figure out how to play a part.
Of course the marketing for the card is going to come up with example of when you need to stream huge bit rates.  They marketing materials say that it is 8x better in 8k than an 850 pro, but the 960 pro is over 5x faster than an 850 pro, so the gap isn't too huge.