I'm not positive how hard this would be -- that's a question for Keith, really -- but I do want to say that I'm very much behind this idea. My main concerns are:
1. There are a variety of difficulty settings (each individual faction, etc), and we don't want to bake that into the scenario. Some people would want the equivalent of 10/10, others would want the equivalent of 7/7. So we'd need some way to have a central "what difficulty do you want?" dropdown that then gets fed into all the factions.
2. Honestly, the map style and size I think also should still be chooseable. So basically I might want to play the great train robbery on map X, and you want to play it on map Y, and that's fine. Maybe it has a default built in, but I shouldn't be forced into it.
In general basically I feel like people should be able to JUST play these scenarios and have as rich an experience as anyone else. I might just wind up playing great train robbery over and over again for 200 hours, but each on is vastly different just like some other configuration of the game is. Obviously I hope that people branch out more than that, but at the same I feel like this is the most interesting style of quick start.