I am quite interested in HBM and how that will work and having a first hand play at it. It can stack between 4 and 8 times, so 8GB is a given really. I am sure there will be some bugs to start but I can handle that.
This simply isn't correct. You're talking about the actual number of memory chips per stack. To start with we have two known HBM specs
HBM1.0 4hi stacks(4 chips max) 1Gb(256MB) chips, 1GB stacks with 128GB/s @ 1Ghz.
HBM 2.0 4-8hi stacks, 1-4Gb chips(256 to 1024MB), 1-8GB stacks with 256GB/s @ 2Ghz(clock speed might be wrong there).
More stacks per interposer = lower yield = higher cost. What the realistic limit is no one knows, what the price of one stack is, no one really knows, what spec of chip will be available, no one really knows. The realistic minimum based on the minimum specs of HBM are 4 stacks of 1GB giving 4GB @ 512GB/s. The reality is any one of the 'upgrades' listed in HBM 2.0 can be done before HBM2.0 is scheduled. That is just a target list of updates. A 4 hi stack using 2GB still at 128GB/s would only meet the HBM1.0 specs, doesn't mean it won't be made.
Effectively HBM could have been produced some time ago, 2Gb chips(needed to get 2GB per stack) have been available for quite some time. It's more than possible we will get 2GB per stack. It's less likely but still possible we'll get more than 4 stacks on a interposer, depends on costs.
That's what I want to see, an 8GB flagship, more grunt, a decent amount of vram to stop any drops or stutters.
This really is taking to long though, hurry up and launch it already !
Again simple reality is that the majority of sales of any card at any level right now goes to gamers who don't have 4k screens. If only 3-4% of sales go to people with 4k screens, do the 96-97% of the rest want to spend more on a 8GB version over a 4GB version? Answer is, not really.
What we'd hopefully see is a 4GB version sensibly priced and if/when higher density stacks become available they can offer a more expensive 8GB version for those who need them. If they are available at launch, great, if they have to wait for those chips to be available, that is how it is. AMD can't magically provide something not being produced. The alternative way to make sure of 8GB is to have 8 stacks and 8GB on every card, which for most people will just be poor value. It will increase the cost quite a bit beyond the actual price of 4 more stacks(due to the yield issue).
Think of it like this, AMD could not offer a 40-50% faster card with HBM this year and lose sales while waiting for 14nm and higher density HBM. Or they can offer a card that only has 4GB, which even incredibly conservatively stated, all 80% of the market needs, and take sales with that much faster card. Then offer an 8GB next gen card at the same time anyway. They can't lose out compared to what they offer today, by only offering a 4GB version.