In the latest community Q&A, the guy named fat jeff asked them about the assault and mentioned he works on it himself with the help of the couple other people. What devs said
-they're not working on it, there's no time for it
-some people want assault with vehicles, some without so it's in players best interest to make it the way they want
-their help with assault development will be limited to making sure it's possible to develop new game modes.
Also, the focus for them now is 'improving' the stuff that's already in the game, like spectating, post match stats and highlights and hitboxes.