J-31 is SAC only, as confirmed by AVIC president himself in a documentary/talk show on CCTV. However, it was probably only self funded in the early stage. Those planes are not cheap to develop. At certain stages, it would be financially and technologically impossible for SAC/AVIC to do everything on its own. Projects of this magnitude need institutes from across the country to contribute in terms of research and manufacturing support. Not to mention the billions and billions of dollars needed for all those.
And as for export, it probably will eventually be exported. This is due to 2 reasons;
1. It's not a backbone/high end fighter like J-20, so there's is no worry of leaking top end tech.
2. It's cheaper, Pakistan can't afford 50+ J-20's and neither do they need something of this caliber unless India received PAK-FA.
Here is my personal guess about the status of the J-31 project,
please tell me if you think it's completely off the mark:
- SAC built the prototype for the "stealth fighter" competition the J-31 lost to the J-20
- there is still interest in the J-31 in the PLAAF/PLANAF (perhaps for carrier aircraft),
but not enough demand to justify the billions necessary to fully develop it
(I guess you would need to build >100 fighters to justify the investment, just building
a small number for aircraft carriers won't be worth the cost)
- SAC is keeping the project running and hopes that the demand for a "cheap stealth"
aircraft will still result in an official project to fully develop the plane
- I think SAC is hoping that if an export customer is interested in ~50 fighters the
people within PLAAF/PLANAF in favor of the J-31 might be able to justify financing
part of the development and ordering some planes themselves
- I don't think an export order of ~50 planes by itself would justify completing the
development
