China was my first thought too, but there is a lot of risk with that. Western countries are these days now unlikely to be at serious odds with each other as they share so many economic interests and goals. So it's unlikely, that the UK will ever boycott USA or Australia (for example).
With China, it's different. They are trying to become the world's dominant superpower. They do not have shared economic interests and goals with western countries. Right now the UK and America are trying to ban Chinese internet and telecommunications companies because they are suspected of being used to hoard data for spying purposes.
Holding a Grand Slam in China would probably be like having one in Russia during the cold war. Because there is so much potential friction with China and the west (Coronavirus doesn't help either), it's easy to see a Chinese Grand Slam one day being subject to a political boycott.
It sounds like a good idea initially because China has so much money and influence right now, but it could easily end up as a mess and a political hot potato.