Let me throw in another variable into this discussion. But first a definition. Trail braking to me is trailing off (slowly releasing) the brakes. That said, let me try to make a point or two.
Increased downward pressure on the front tire increases available traction on that contact patch. A simple experiment will prove the point. Lightly stroke a pencil eraser over a smooth surface. Repeat that several times with increasing levels of downward pressure on the eraser. Which stroke provided the most traction--the light or heavy stroke? My point here is that by keeping some forward weight bias on the front contact patch with trail braking in a turn, you are actually gaining available traction on the front tire over what you will have with a rear bias when accelerating.
Now repeat the experiment but add lean angle. You should be able to observe that when lean angle is added, our downward pressure on the pencil is not as effective at increasing traction. When we add lean angle, our pressure is a combination of down and lateral pressure. That tells me that I need to be careful my expectations of what trail braking will do for my traction as I add lean angle.
How does this apply to braking on a motorcycle? For me it is that my heavy braking will occur while I have no or very little lean angle. As I increase lean angle, I will have to decrease brake pressure via trail braking. Why not just get all my braking done before turn-in? Mostly because the optimal slow point of a turn may not be the entrance and the bike steers better with weight on the front contact patch.
Of course there are limits to everything. Front suspension travel and lean angle come to mind in this instance. However, the rider with the ability to operate up to those limits does better than the rider who is unwilling to approach the limits or the one who exceeds the limits (wash-out). So, the rider who understands all the variables and hones their skills well enough to use them becomes a better rider than the one who wants hard and fast rules to govern their actions.
Does trail braking into a corner work? Yes (as someone pointed out, the top riders use it regularly). How well does it work? Depends on how well you employ it.
To me this is not about whether one should trail brake or not. I just see it as another skill I will have to master if I want to be the best rider I can be.