Adding an optional UnionPay card linked to your CA could be super beneficial for travelers to China as that is accepted everywhere compared to maybe 20% acceptance of Visa and Mastercard and also could be a differentiating trait as currently there are no other UnionPay issues in the UK afaik.
Their exchange rates are also not too shabby:
http://www.unionpayintl.com/cardholderServ/serviceCenter/rate?language=en
That would be awesome but I’m not sure joining another global payment network is that easy.
If you want a UnionPay card, look at ICBC.
There are dual branded cards in some countries with both Mastercard or Visa and Union Pay. They work on Union Pay in China and Myanmar etc but on the normal card scheme in the rest of the world
UnionPay (non-dual branded) ones are working globally in 162 countries according their website and it is true that most UK terminal accept them.
Also I found this list of foreign (e.g. outside of China) issuers: