I would suggest that you make temporary stops count towards the train limit - or at least the option to do so for interrupt stops.

This would allow for simple generic delivery trains via interrupts, without sending 50 Trains to Iron Mines only because one Station needs iron. For now the only way ...

I absolutely second this! I would love to see this as a feature!

While there is a quick fix (just connect a constant combinator beside *every* station, and use Signal Parameters Instead, this is annoying, and maybe you want to use the signals for something else...