The problem with the application being online is that in a foreign city of a foreign country, where a public transit app is most important, you are roaming which costs like hell. So a primarily offline application is, kinda, must.

Second, what if you just document carefully the data format used and enable the application (if not already) to work with multiple databases? I think those who find a way to scrape the data from services will let you know they can, once you advertise it.