I'm also curious to see how GDDR6 will stack against(pun intended) HBM2 outside of consumer/gamer applications as well. I think HBM still has a while to go before becoming mainstream so I personally think while 6 is gonna be expensive, it'll be cheaper still than HBM and therefore be on every Nvidia card in the foreseeable future.
I think AMD will shoot themselves in the foot and stick with HBM for the high end. They have become so architecturally attached at this point I don't see them ditching there designs and doing a complete flip flop.