I don't think Big Navi will have HBM, it's still too expensive for a gamer card, but when it comes to how much memory it will have, I honestly don't know. Higher is better, of course, but also more expensive, and GDDR6 isn't cheap to start with.
Please excuse my bad English.
Currently gaming on a PC with an i5-4670k@stock (for now), 16Gb RAM 1600 MHz and a GTX 1070
Steam / Live / NNID : jonxiquet Add me if you want, but I'm a single player gamer.