"I think it's important to note that all of this is pretty minor. We've tended to make mountains out of molehills where handling is concerned, especially when the discussion is about trail."
I'm quoting myself because I am even more convinced of this now than when I wrote it. I have continued my experimentation with trail and handlebar bags and am firmly convinced that trail makes a very minor difference overall. I believe the handlebar bag makes far more difference to handling than does trail, and am coming to the opinion that most folks who don't like handlebar bags don't like them because they are improperly mounted. A bag swinging from the handlebars -- as opposed to firmly mounted to a low-riding rack -- is likely going to create unpleasant handling regardless of geometry.
My current brevet bike has very low trail, with geometry copied exactly from a 1950's Herse. It rides very nicely with a bag. I recently swapped it with a mate's Rivendell having higher trail than any bike I have ever ridden. It also had a properly mounted and fully loaded handlebar bag. It rode almost identically to mine, at speeds from 6 mph to about 35. Out of the saddle handling was strange to me and I wobbled around on it a bit -- which is exactly the same thing my mate said to me about mine. Bottom line? Given time to become accustomed to the handling of either extreme, I am sure that I would be perfectly satisfied with either.
I still have a lot of respect for Jan Heine and really enjoy his stuff -- but I do believe he has concentrated on minutiae to the point that, to his readers, it looks far more important than it actually is.