There was a great drawing put up by gringeltaube on this very subject if you are into searching for it. It clarified in simple terms as to why it is preclusive (not impossible, but preclusive) to install a seal that is adequate to contain gear oil in a hub and axle assembly that was not designed for such.
Personally, (and this IS subjective on my part) I believe that if these axles were built today and designed with an oil bath hub in mind, I think the wheel bearings would have longer rollers for a larger bearing surface, and they'd be like lots of modern ones with a service drain/fill port separate from the main axle resivoir, just as modern ones do when the oil level is too low to guarantee that they are refreshed from the main reservoir.