Presumably they just mean that the GDDR5X memory is not optimized for the ETH algos in current mining software. So, there are probably more profitable ways to use your card mining.
I see. I didn't know that and I assumed this was about which card has the best hashing-rate/card price ratio. Currently, I'm getting pretty stable ~40MH/s with GPU temp of 52 C. Looks like it could be a bit more profitable to mine Zcash with GTX 1080 TI...
Sorry for the off topic and hopefully we get the next block soon.