They probably use MiG-21's engine while aircraft is in development, I do wonder since wingspan is comparable to RQ-4B yet main body is dimensions of RQ-4A then could it be extended to be comparable to RQ-4B if engine used in MiG-29 was used to propel Saetbyol-4.
Since if R-25 was used then that is 40kN of dry thrust while RD-33 has 50kN. Latter consumes same amount of fuel in full operation while providing 25% more thrust than former. They could extend main body and perhaps increase fuel load by 10 or 20 percent.
Overall flight time of Saetbyol-4 could be doubled and more aerodynamic as it would not need cooling intakes for turbojet engine.
Though I wish they import a lot of SM-100 engines though best case is licensed production that is transfer of technology.
Since two of them even with afterburner section would be same weight as RD-33 yet have many benefits over it.
Such as considerably lower fuel consumption per generated thrust along considerably more thrust than RD-33,
Perhaps 20% better specific fuel consumption while providing 30 percent more thrust with two engines.
But this is just mere wishful thinking. Unsure if Russian leadership is bright enough to see benefits of empowering their allies.
Especially North Korea that would be a force multiplier considering their garrison state mentality(with good reason) of its leadership.
.