In the 5+ min trailer they just released we get 2 tiny glimpses of Barry's father in the scene with his mother and the yellow blur (LOVE that they appear to be going all out with that story, and can't wait to see where they go with it.)
Once in a picture of the family on a side table, and once with him standing with Barry watching what's happening.
Neither one is perfectly clear, and they both go by very quickly, but it looks a LOT like JWS is playing his father.
Regarding secrecy around his role, if he's playing his father, and Barry's ongoing personal mission, above and beyond the crime fighting, is finding his mother's true killer, and clearing his father's name, then that would mean that JWS's role is going to be significant in the long run.