Problem is if you actually want to move forward quickly you need to break out of that square stance, so there's a contradictory tension there with the way wc is taught.
Furthermore, someone standing face-on with you like that exposes their centerline, leaving them vulnerable to getting poped when you take a more staggered angle on them, giving you the reach advantage.
Additionally, if you do happened to get close enough to do the sort of flurrying that is so often shown in demonstrations, the most practical and obvious thing to do at that range would be to tie up with the opponent and work your clinch game. The opportunities where where that would actually come into play are so often transient. Optimal control of distance is either all the way in or all the way out, and there just isn't much of a place for that there.
There are several things that each individually might have situational application, but when thrown together it is a hodgepodge that doesn't add up to a coherent game plan. The best wing chun fighters in the world right now are Andre Ward and Floyd Mayweather.
