d) There are some services which are more operationally convenenient than provided for significant passenger flows, and including those in the spec would tie down the next operator unnecessarily. I would argue against a specification that's drawn up in a way that it forces (or strongly creates an environment for) a less than optimum service as far as passenger are concerned.
Good example came up just a few minutes ago. The 06:48 Portsmouth Harbour to Brighton (arrive 08:15) is cancelled this morning. Quick look on journey check shows that the 06:45 from PMH, change at Havant, will get you to Brighton at 08:18. Being a Saturday, I would expect there to be plenty of room on the remaining train.
Even if there's a franchise requiement to have an
GW▸ unit in Brighton to form a subsequent departure, I contend that it's reasonable to leave it (on Saturday morning at least) to the GW
TOC▸ to decide if the unit runs a service from PMH first, or perhaps an extra North Downs service from Reading to Gatwick and on to Brighton, giving extra strength to the airport for everyone flying away on their Saturday package holidays. Or for the unit to be parked up at Preston Park overnight from Friday ...