I don't think you'd play any different with these kinds of station coverages, you'd just be more annoyed about gaps and overlaps.
They might make more sense if there were really big circles somehow, but why would you have those? Maybe if there was a second station coverage for long-distance-travel, allowing anyone inside the area to go there by local traffic and using that station as a starting point for destinations further away. Basically, this would simulate that someone travelling from Linz to Lafayette would not bother to check local busses, but rather plan the journey from Linz central station or Linz airport - as a city inhabitant, you just assume there is a way to get to the airport or central station.
More in detail, for anyone who bothers:
Say there are three levels of travel, let us call them local, international, and intercontinental, even though those words only work on world scale.
There could be "international" station expansions, and "intercontinental" station expansions which, upon building, give this station an "international" and "intercontinental" coverage according to the stations size. Size could be either the capacity or a new value given by special station extensions.
International stations are only connected if you can go from one to the other without changing vehicle anywhere but in an international station. Once you get two international stations on the map, international travel starts by picking two international stations (probability calculated by the amount of potential pax in it's international coverage radius), and if a route is found, you look for a normal station within the international coverage radius, again based on the number of pax connected to that station, and find a route from there to the international station.
Intercontinental works the same, but one tier higher, searching for international stations first.
The problem of calculating long routes on big maps is that there are so very many possibilities. This is also one of the reasons why there is a limited amount of vehicle changes before the algorithm aborts (unwanted cross-connections is another one)
By using two seperated grids like this, you get far less possibilities. It might be that the number of line changes could be reduced to a small number like 3, and still have connections from anywhere to anywhere on the map. This should in turn result in better performance.
Obviously, backwards compatability is given simply by not putting any international stations in the pakset.