I might be coming into this discussion way too late and at the risk of the mods nuking me, one possible benefit for a 3-engine 6th Gen might be that China, whilst they have come a long way, still does somewhat lag when it comes to leading edge engine development. The PLAAF might not be confident in the industry to deliver a variable cycle engine in the timeframe that they want to start inducting 6th gens to the tactics development squadrons. Having 2 'performance' engines and one 'efficient' engine might be a way to get the jet to both fly very well with incredibly high efficiency over longer ranges (up to crossing most of the Pacific and back) whilst also mounting traditional high-performance jet engines to fight and maneuver well when it becomes necessary.