"So then why not train the forms and drills using this boxing biomechanic that seems to naturally want to show up in sparring/fighting? Again, just thinking out loud!"
Well that's an excellent idea, I think you should do that some of the time, but on the other hand, alot of the time when you are practicing the traditional way you are trying to influence yourself to reduce certain tendencies "and wingchun-ify" your fighting. Let me start with a real extreme example, the low horse stance. You'll ideally and 99% of the time never fight that low, but if it trains you to sink, that's great. Because the tendency when sparring or fighting is to stand straight up with the knees locked. Yes I think sitting in a lower stance than you would actually fight in, can be useful because it trains you against your natural tendancy. When we practice Wing Chun short punches, are we trying to develop 1 or 4-inch punches? No, we're training so that our punches are shorter and crisper, with the elbows down somewhat, because the natural tendancy is to flare the elbows and use too much backswing. At the same time, I think Wing Chun can be overconfident and there needs to be a backup plan, like using head movement as well as one of the "saus." Boxing is also a good framework to understand your Wing Chun with as well, for instance the pak sao is a parry, thinking of the front and rear hands as throwing "1-2s" etc. You have even more of a framework to draw upon if you think of your Wing Chun in MMA terms, common names for your throws like scoop, hip toss etc.
BTW, AFAIK for whatever reason no-one has really used stomp kicks well with damaging effect in the UFC, though I've seen a few guys throw them.
I think of course that the longer you train the traditional way, the more you will see this coming out in your free-sparring. But you need to maintain a continuum of free-sparring so you aren't shocking yourself out of your good habits when you jump in.
heck, I always had trouble with just "hands up, elbows down, eyes wide open" when under fire. It takes time to get to where you're comfortable in the ring/whatever. One thing I was able to do for the most part is to utilize the basic wing chun steps, not all the ones you use in Chi sao and the wooden man but the basic marching steps, the half step and the exchange step, step left, step right and in some occasions the triangle step.
Oh yeah, I recommend to anyone, no matter their training philosophy, to come up with some Wing Chun drills ( trapping hand drills for example ) that end with punch or punches to a focus mitt held by your partner. This way you get used to hitting something.