Would it have been possible to have a special lug fabricated that would act as a go-between with the seat stay and the non-mixte dropout? It seems that it wouldn't take much to produce such a lug. The old Raleigh lugs were just stamped out and hammered together and welded (and then not really cleaned up -just faced so it was hard to see the seam) It might even be easier to have done this than trying to put those tig welds onto the cast dropouts which, like you said, looked confused and sloppy. This is hand-work either way -but one is more skilled handwork than the other and looks like it when the finished product is surveyed by the appreciative connoisseur.

I guess it comes down to money/costs and a general lack of interest in the mainstream buying public. Today's typical consumer just doesn't care about these things. Bicycle "fads" like the emergent mixte craze might be driven by such as the enthusiasts on on this forum and readers and writers of blogs like Lovely Bicycle and Rideblog, but most consumers can't tell the difference between a beautifully-done lugged frame and something slammed together like the interior plumbing behind the tile of your shower wall. For the most part it isn't worth it to most builders outside of Rivendell or a few high-end top-$ makers to give us what we want because the price-point most consumers are willing to pay just don't match the low-end builds that competitive frame and bike builders who populate the mid/low-end market are producing.

Today's buying public is used to junk/disposable products at bottom-line prices and are just not willing to spend a bit more for something artfully done. This creates a market for low-end garbage and makes the high-end quality product even more of a premium since the economy of scale is just not there any more at that level and the competition for the elite buyer doesn't give such pressure to keep prices lower.