Could railway overhead wires be used for long distance electricity transmission?

Most electrified railway in Europe operates at 15 kV 16.7 Hz AC or 25 kV 50 Hz AC.

Power is typically produced between about 2.3 kV and 30 kV and stepped up to 115 kV to 765 kV AC for long distance transmission (Wikipedia).

If the railway overhead wires were fed by a single power source how far from this source could the rail network extend?
Is there a limit to the number of users that could connect to the railway overhead wires?