I like the concept. The main difficulty I see with a 2 ipc rule though, is that the some of the major transcontinental railways that existed at the time would violate the rule (by passing through 1 ipc territories.) The Trans-Siberian, Trans-Canadian, Tran-Australian would all be out for example.
Something along the lines of what Narvik suggested might be workable, but there the issue would be max capacity of the rail lines. For example, it’s conceivable that some units could be redirected from one end of the rail network to the other, but not all units at the same time. So would there be an upper limit on how many units could move around like that, within the broader region they control by rail?
It might be interesting if the total rail capacity was somehow related to total production capacity of a Nation. For example, if the max number of units that could be moved around like this, was limed either by your total IPCs or by the number of nearby factories, or something of that sort.
The idea of caping the movement at 2 for all ground units would fit with the concept generally, but would definitely diminish the value of tanks and mech as others pointed out. A bonus of +1 to all units, is another alternative, though this would dramatically increase the value of tanks and mech. Its an interesting trade off, but on the whole expanded movement makes me a little nervous. It really needs to be handled delicately, since it’s much more powerful than expanding say attack or defense values. The long range air tech, or ABs have been an example of this, and they can be very potent, and crazy game changing.
I still like the idea of a rail base though, or some kind of rail component to the factories, or ways for Infantry to move at an accelerated pace under some conditions like those.