During the livestream earlier this month it was already announced that Nvidia would be allowing board partners to release GeForce GTX 1060 and 1080 with updated (faster) memory. MSI is the first with info on this topic, the new PLUS SKUs.
Basically the Gaming X models of the 1060 will get a bump towards 9 Gbps GDDR5 memory. The 1080 SKu will get its memory clocked at 11 Gbps. For both cards that is an extra ~10% in memory bandwidth. Unless the boards are clocked faster, we doubt a little if the increase in memory frequency will have a substantial enough performance increase.
It is a bit unclear when these models will be available, we expected them this week already TBH. However it seems that will be early April then. Prices have not yet been announced.
MSI To Release Gaming X PLUS GTX 1060 and 1080 with Faster memory