Actually just putting this idea out there. It is not that China needed Su-35, they have other fighters out there that can roughly match up with Su-35's capabilities. However, for political sense, I believe it would be a good way to renew China-Russia relationship, buying one hundred Su-35 is giving money to a friend in needs and if China can afford it, why not? Please I really do not believe that Chinese cannot get anything new from Su-35, they can still learn something that might be of great help with upgrading her aging fleet of J-11s.
First of all, Russia is not a friend. They are a short-term asset and long-term headache. Simply giving them cash without getting something worth in return is beyond stupid. The Su-35, in its current form, is not worth. So either they changed it drastically to attract Chinese interest or the deal is entirely bullshit. This urge to "please" Russia or any foreign country because of a temporary realignment in power is a mental disease that needs eradication. China shouldn't have to set herself on fire to keep her allies warm, and Russia isn't even an ally.
Secondly, why on Earth would China need, of all countries, Russia's help with upgrading airframes? Russian standards of manufacture, maintenance, customer service, and all-round quality are incompatible with PLAAF requirements. Everything the PLAAF is doing for their Russian equipment is not what Russia is doing for their own equipment. Russia leaves their fighters out in the open, which is fine for them because their climate is dry as a bone but do that in tropical Fujian and you'll find Chinese Su-30s start achieving IAF-levels of attrition. Russian AL-31F maintenance procedures were so old-fashioned that when the PLAAF constructed their own overhaul facility, AL-31F lifespan went beyond original specifications. Additionally, Su-27SK FCS was so troublesome that China cracked it and integrated their own upgrades to support indigenous ordnance. So unless they're going to install super-duper technology into the old J-11 airframes for a bargain price, they have nothing to offer China.