1. Sony had already designed a console around GDDR5. When densities doubled, they simply doubled the allocation because they did not have to change anything in design. This is not the same as what you are proposing.
2. There is demand for HBM.
Samsung was on record as saying that they could double output but it would still not meet demand. if Demand>Supply, then prices have to be high because there is more money in contention for limited goods. If Supply>Demand, then prices drop because there are more goods competing for limited funds and manufacturers need to undercut on price......in fact, producers are likely to try and drop prices to stimulate demand.
3. These consoles are being built to serve as mass market devices. There is always going to be a bigger emphasis to try and bring costs down more than there is to innovate if that is going to drive costs north. This is why we are unlikely to see the fastest chips on the market, or the most expensive solution. It is why you are no longer seeing bespoke chips on the market like Cell or Xenos. It is, let AMD do it, and we will customize some aspects.
4. I am not in the engineering field, but I read quite a bit when I have the time. One thing that is common is that companies do not like running over budget or making changes unless they feel they are necessary. What is the advantage of going HBM over GDDR6? What is the cost, and how is that cost going to be recouped?
Everything that goes into these consoles costs something, and the consumer either has to bear that cost, or the company has to bite the bullet. There is always a chance that they might choose HBM (simply because it is an option), but HBM3? How would they be designing a console on something that is not yet in production? How would they test chip samples to see what needs to be tweaked?