I couldn't bring myself to read this thread all over again, but if we are talking about adding a few mm of rake to a 47mm offset fork, such as is found on the majority of touring bikes with low rider mounts happily carrying 40-60 pounds on the front end in order to carry 15 pounds, then I think there is an ailment known as "too many issues of Bike Quarterly" in play here. Sounds perfect as is. My last touring bike had both low riders and a porteur rack on it, carried on a 45 mm fork, narry a problem. Of course my next bike is going to have a 70 HT angle, and a well offset fork, just to solve the kind of problem I wasn't having.
I'm not sure the extra 8mm of wig waggling of the fork will really hurt anything, but I think it's a fools errant, most likely anyway. Of course a lot of custom detail probably fall into that category so ya gotta do what you gotta do. Just slide it under a good solid door and heave.
My observation over the years is that the "real" frame builders are a pretty conservative lot in the good sense of the word, but it can be a tough crowd to get support from.