The Marston Vale line runs between Bedford and Bletchley, the stock used on this line is the class 230 ex london underground D78 stock. This train is kind of in the game as the class 484 i think this would be a welcomed route to the game Stock: Class 230 Operator: London Northwestern Railway
you need to write a bit more about it and add photos e.t.c and personally I would prefer this route with the LM 15/1 and 153 but the 230 is cool
Like Sam I would prefer it done when the sprinters worked the line and then it would be of interest to me.
It would be a nice little branch line to explore, but as Vivarail have now gone bankrupt that might prevent seeing the Class 230 in-game perhaps. The Class 150/1 would be a good alternative choice, but we won't have anything to populate Bletchley for AI services currently.