The Abbey Line is a branch that runs for 6.5 miles between Watford Junction and St Albans Abbey. For the last couple of years, the service has been operated by London Midland liveried Class 319's, although this has recently been taken over by Class 350's occasionally. All in all, it's a very simple and easy route to do if Dovetail need to quickly send a UK route out to stop everyone whining about when the next UK route will be. Personally, pricing should be around £9.99 - £14.99 with anything above probably being a bit extortionate for a line of this size.
I said yes, too short but what if it were done as Euston to Watford Junction inc the slow lines (313s on the slows and the Abbey Branch and 321s on the fasts) or 350s on the fasts and 378s on the slows and the branch)
Very short and the best bet for is combining it with West Coast Main Line south Milton Keynes to London Euston or retreating TS 22 version West Coast Main Line South Birmingham New Street to London Euston via Birmingham Elmdon Airport railway station
I said yes, not just because of the physical length of the line, but because is ends at a station which people would want populated, which wouldn't happen in such a small DLC. Better to have this as a branch from the mainline or as a minor extra DLC somewhere down the line (ie not likely to happen)