Hi again Cyaoeu !
Yeah I think that sort of stuff is definitely possible. Overall the system is quite remarkably open (with Blender being tweakable at will, and the retargeting tool inside UE4 being very robust). Epic is definitely doing a good job here. I personally believe that the absolute best would be for Epic to create an importer working directly with .blend files + a very clearly established reference scene with a pre-made skeleton in it (with the hypothetical importer taking care of converting bone orientations on import). I feel like this will have to happen sooner or later !
Don’t hesitate to let me know if you need any testing whenever you dive back into that sort of stuff, I’d be more than happy to help. As a matter of fact if you already have a Blender animation file using an intuitive performer skeleton I’d be very interested in playing with it to see how far manual retargeting to the Epic Skeleton can be pushed in Blender using delta bone constraints.