This sounds a lot like the on-demand(ish) bus service called Bridj which just shut down here in Boston. [1] They promised popup bus routes just like Citymapper has, but it ended up that a lot of the "routes" they constructed were essentially missing gaps in the MBTA's bus/subway system.

The bus route generation tool that they mention seems to be very promising. Hopefully the realtime demand data is the piece that Bridj was missing, as it would be very cool to see this kind of stuff take off in other areas. I wish them all the success in the world - hopefully this works out for them.

[1] https://www.theverge.com/2017/5/1/15501764/bridj-on-demand-b...