While this is a very fair point, the Merseyrail line(s) offer an attractive package to DTG to make. It can be split into two packages (Wirral and Northern), each offering a variety of routes over a small-ish network. Each of those full legs range from 20-60 minutes each so again makes a nice variety and a frequent timetable to boot. It also offers - admittedly small - bits of underground stations too for Moorfields and Central on the Northern line, and a few stations on the Wirral line, including Central (Low Level). It'd also be nice to "preserve" the 507/508 fleet as they're retired in real life as well as getting the upcoming and modern 777.