A350 for P3D will never be a thing, all developers moved to MSFS/Xplane 12(not yet), so you only have merges for now, for future a350 is nowhere to be found
Digital Flight Dynamics are working on a freeware study level A350 for MSFS. For XP, there's the Flightfactor A350 that you can check out. It has Aerosoft Airbus levels of systems depth if that's what you're looking for