Considering AMD has experience w/CPU's that support GDDR5 why couldn't they release a Ryzen CPU that supports GDDR of some type? I guess you would have to have motherboard manufacturers willing to design motherboards w/a fixed amount of non-removable GDDR5 but wouldn't the performance gains be worth it? Doesn't GDDR5 out-perform the highest tiers of DDR4 right now? It looks to me like the highest performing DDR4 kits now would only produce over half the bandwidth of a GTX 980 (224 GiB/sec) even with a quad channel setup because even Samsung's latest LPDDR4 modules only produce 34 GiB/sec for each module:
I don't know but I'd rather see HBM cache on-package.
It would be best to still have the option to insert DDR4 on the motherboard.
If they were to manufacture motherboards w/say 8 GiB to 16 GiB to 32 GiB of on-board GDDR5 you could buy whatever you need. For me, my CPU's and motherboards become outdated far before my RAM and aside from increasing the amount of RAM how much perf. difference do you get going w/the highest performance DDR4 or DDR3 memory you can get as opposed to the bottom tier? I once tried replacing my DDR3 memory on my old LGA775 board w/higher perf. memory and it didn't make any difference in gaming performance.
HBM is an interesting idea, especially in the 16GiB range, but I don't think any AMD CPU supports that tech right now.