I'm surprised at so many of these players going to China but I don't think it's sustainable. I've done a lot of travelling in China and also lived there as an ex-pat for a while, in one of the more 'westernised' and modern cities. Here's why I don't see this being any more than a fad:
The language is rock hard, probably the hardest I've come across - they'll rarely if ever need it though. The food, can be weird, but again they'll be eating at the top tier and can choose whatever they want.
The sport is not very popular. The Chinese love basketball but in general, China doesn't have much of an affinity for 'team sports' - they seem to prefer solo sports like table tennis, athletics etc.
The nightlife is effing abysmal. Outside of Shanghai and Beijing, the nightlife is the worst you've ever come across - I don't see a footballer used to going to hip, trendy nightclubs with strict guestlists and hoardes of willing wannabe wags getting wasted...warming to the sort of gaudy, tacky, sterile atmosphere you find in the major nightclubs in China. They will not enjoy themselves. China simply doesn't 'get' good nightlife.
Basically, I'd bet that 9/10 of these players arrive, see the quality of competition, see how unappealing the nightlife is, and resign themselves to it being a quick, massive payday then jump ship.