I have several synthetics and I can say that synthetics will not overpower the market any time soon unless there is further evolution in the fiber construction.
Synthetics are good because they can easily lather anything out there, and they can produces lots of lather fast. The issue is that there are a lot of bad soaps that can't be lathered well with badger/boar brushes, and so folks are buying synthetics because they work better in that regards. For me the face feel of badger is still not achieved by any available synthetic. I have tried the Plisson knot in several sizes and lofts and none has been close enough to how badger feels on the face. From my experience if one wants more backbone then the knot has too much scrub and not enough splay. If one wants more splay then there is not enough backbone. With synthetics it is a bit of a game of compromise, that never happens with a badger, there is always an option that combines good backbone with splay with/without scrub. My current favorite synthetic is Simpsons CH2, but not at the factory set loft of 52mm. I had mine transplanted in another handle at 55 mm and it not works really well. My second go to synthetic is a 30mm WD which has a very good combination of backbone and splay/scrub. To get that effect I had to set it at the highest loft I could and there was not much room to play with .
If the industry can produce fibers that have thicker shafts that taper towards the tips then I can see synthetics becoming pretty equal to badger/boar brushes.