FRA considers it "main line rail", not "main track" though I used that term in my previous comment. Your definition of "usage=main" is arbitrary, ambiguous, and subjective. The FRA has jurisdiction over that track, not OpenStreetMap, and OpenStreetMap should reflect the FRA definition. OpenStreetMap may indeed be right 95% of the time, but FRA is right 100% of the time. I've indeed tagged "usage=branch" or "usage=industrial" as appropriate. I've also tagged that track as "railway:track_class=4". Why don't you contact the FRA with your suggestion? When the FRA changes their definition, then I'll update the map in accordance with the FRA. To be clear, I changed the South Shore Line to make it show up on the max zoom level at Open Railway Map. It'll be a disservice if I were to revert the changes without appropriate guidance from FRA.