Hi Charles. Since we all now mainly "focus" on the new simulators
KRS:
http://www.railsimulator.com/
and MSTS 2:
http://www.microsoft.com/games/trainsimulator/
i doubt the possibility to do any "new" routes in the MSTS, would be very limited.
But if someone should build a route as you wish from Stockholm and Falun, i guess it would be done in KRS or MSTS2.
Sad to say, but i think we can only expect a minor number of new routes or other content for the original MSTS in the future, since KRS is released in the next month. Life goes on...