This is pretty simple. It made is to make routes more realistic. The trains will be sold by country. For example the US inspection Trains would be for all of the American routes. Majority of inspection trains are pulled by modern engines but old passenger cars. Most of them are three cars long and would be easy to make.
Why not do one for European route and network Rail United Kingdom rail infrastructure manager has HST and Class 313. Deutsche Bahn Germany ICE-S ICE-TD.
You mean a modified West Cornwall local Class 150 to serve as an infrastructure train. For SEHS St Pancras to ebbsfleet station and LGV Mediterranean Line Avignon-Marsellie TGV Iris 320 is used