Their insentive is they have let it go about as far as it can go, it isn't Iran's feelings they care about. there is no evidence China has supplied them with nuclear material but we know they have sold them some of what they need to create it.
China may go for deal where Iran can have nuclear power but it all has to be totally open to UN inspection and subject to conditions , it would be like China to not back down once they take a stand. the UN can't ever get Israel to abide by a resolution so don't expect China to demand any more fron Iran, nobody has right to deny Iran or anyone else the right to nuclear power and this is where China has been going with this. they're right, but they're also going to be responsible for what it's worth if things go bad and as long as this regime is in charge of Iran it will.
Don't worry nobody is going to come down on China with anything more than a scolding, nothing more. and they know it.