Some good comments here.
TfL’s official stance is that the dotted lines are there to indicate nearby stations, not just to highlight interchanges. My OSI list already indicates the rough distance between stations so I don’t really see a point in saying whether the link is dotted or not. I also don’t really want to highlight non-OSIs as I think that’s confusing. Better to get them made into OSIs and then add them to the list.
Also, if Caledonian Road is shown on the map, Bethnal Green (LO) to Whitechapel (LO) also should be as they’re the same distance according to Google maps. I’m sure that would also get quite a bit of use as an avoiding zone 1 option. They’ll have to redraw the map to show it though.