Question is what it's for. A proper transport layer on the map would be valuable to me. Even without timetable data. That's even in relations on openstreetmap already.
Next improvement might be to highlight lines based on frequency of service. Still possible to precalculate with little need on device.
We'd love to have your input for improved transit in CoMaps! I agree it's an important priority. Last GSoC there was a project for ingesting GTFS feeds against OSM data, since local agencies are often much better about their details than OSM is, but as a student project it was slow and limited in scope.
E.g. Motis needs walk routing data that weights hundred of gigas.