I've heard rumors that Discover was developing its own breed of DCC, but for now Union Pay terminals do not have DCC functionality.
Regarding your point about chargebacks being annoying for my bank, you're probably right, and they are certainly far more costly than the amount of most disputes (i.e. I used to flood them with batches of 100 receipts at a time and let them figure out the differences between the DCC and spot fx rates), but it's not like BoC, HSBC, or 交行 would ever care about Charles Schwab Bank's opinion.
HK used to be far better than China (i.e. mandatory DCC was rare), but I've noticed that it is starting to spread there at an alarming rate as well, which I suppose shouldn't be too surprising because many Chinese acquirers also operate in HK.
In the China forum thread, we've posted DCC workarounds for several popular POS machines. The problem is they are continuing to "innovate" faster than us.