Ldp
2
I have not tried the plugin, but have a quick question:
What gets added to the associatedStreet relation? The interpolation way, or the addr:housenumber nodes therein?
But: bloody brilliant! I just mentioned needing something like this in JOSM to a few ppl on #osm-nl, and look what you cooked up! Great! 
PS: We would also need a way to add further addr:housenumber nodes (that are inserted into the interpolation way) to the appropriate relation as well.