Well, "correctness" is in the eye of the beholder. People have different agendas and expect different things from the map. In this situation there is a conflict between the visual look of the map and the need to express some constraint about how traffic may be routed.
I agree. If the map was purely intended to support Garmins, with whatever limitations are in their routing functions, then I think it would be a change worth making. But another group (Tomtom, etc) might have a router that supports ways as the via, so they would be able to make the most of a map that looks good _and_ has correct routing data.
So, for the garmin, I am not sure that restrictions that have a Way for the 'via' member can ever be supported. Put it this way, if I knew how to implement it, I would do it anyway even if it wasn't actually very useful.
It'd be a real shame if it wasn't possible, even if there's only a small number of realistic cases. I wonder how the Garmin paid-for mapping solutions model the same situation? <...goes off to think about it some more...> Keep up the good work. Alan