Pakistan can't afford a plane as expensive as this, unless China gives it to Pakistan through loans (de jure) but really just gifts (de facto). Any warplanes wouldn't be effective unless there are large number of it, even for the mighty F22. If Pakistan wants to match Indian Airforce's dominance in the region, they would need at least 100+ of those birds, that's still assuming India doesn't have PAK-FA yet. If Indians do have PAKFA, then they'll need few hundred of those planes to just even catch up.
Like I said weeks ago about the JF17/FC1, China doesn't have that many allies or long term clients. For those that they do, they're all too poor or too small to need weapons this advanced. Those that are rich enough and a heavy industry to support it, are all under international embargo. Now comes the J31, which is even more sophisticated and costly. The only ones that want to buy something this advanced includes Iran, Thailand, Pakistan, North Korea, Egypt, Venuezuela, and the Gulf States. But there's an even bigger problem. Iran and North Korea is under international sanction. Thailand and Egypt aren't desperate for something this advanced, their F16's are suffice; especially their problem is internal rather than a external military conflict. Some Gulf States did buy weapons from China, but those are small batch low budget army howitzers. Nothing as big as warplanes. Most of the real big buyers would only buy from EU/US. Pakistan and Venuzuela are the only remaining two. Although Venuezuela does have big cash reserves, they have a tiny airforce and doesn't show need to expand it.
But as for Pakistan, the Pakistani ground crews will only be able to do basic maintenance. Any big overhauls or deep maintenance, especially when involving the radar absobent material, will require the plane to be sent back to China.
So China can't really export J31 at all. The best they could do is "give" it to Pakistan.
Chinese strategists and planners are not stupid. It's impossible that J-31 was privately funded and intended for export.