Freight trains are usually slower and make long stops, thus not very convenient for passengers and it likely would not really save much anyways.

You mean something like this?

GmP = Güterzug mit Personenbeförderung (Freighttrain with Passengertransport) PmG = Personenzug mit Güterbeförderung (Passengertrain with Freight transportation)

The first had a very slow timetable. On every station the passengers had to wait for freight-car manipulation.

The second could not transport that much freight, but it was faster for passengers…

It is an idea of the beginning of railway-age.