There have been plenty of Nvidia Geforce GTX 1080 Ti rumors lately and the latest one suggest that it might ship with 10GB of VRAM.
Spotted in a shipping manifest on Zauba.com, the alleged GTX 1080 Ti has the same PG611 board name, which suggest it is based on GP102 GPU. The entry has a shipping manifest that is different than Titan X one and comes with 10GB of memory.
While usually it does not make sense to have a 384-bit memory interface but,
as pointed out by Videocardz.com, this is not the first time that Nvidia is using more memory controllers than it is necessary, like for example on GTX 660 or GTX 970.
Of course, this should still be taken with a grain of salt as Zauba ships plenty of prototype graphics cards so this might not be a GTX 1080 Ti after all but it surely lines up as the GP102 equipped GTX 1080 Ti is indeed coming and it could easily end up with 10GB of VRAM, which should place it well between the Titan X and GTX 1080.
Source:
Videocardz.com.