Given the current time, list the positions of all vehicles along a particular route. I'm not sure if it's possible to estimate the lat/long for the point between two stops given a route and its shape? Maybe this is more complex or not required.
List all stop locations (lat/long) along a particular route.
List all transfer locations with options (lat/long) along a particular route.
Having a list of sql and orm queries could help users.
https://stackoverflow.com/questions/30419707/sample-gtfs-sql-queries (just found this one):