J-10 export issues are also based on the Al-31 engine powering them. J-10 sales are basically in competition with MiG-29s, and the Russians wouldn't like the export aircraft coming into the air. So an export J-10 requires a Chinese-made engine to power them. But even if you see J-20s flying with WS-10G or other variants, that's no guarantee that the WS-10 is mature enough for a J-10. While the J-20 is obviously a higher performance aircraft than the J-10, it's a dual-engined fighter so the reliability requirements are far lower than for the J-10, a single-engined fighter where an engine failure could bring the aircraft to ground uncontrollably.