Few questions:
Do you think that will involve attack too? I mean if unit A has in front a plain and a hill with unit B, can we assume the unit A can only move to plain then need to wait next turn to attack ? Or the other way around?
Also what would be the final goal of this? I mean hills were definitely strong in melee but if the above is the case they woudl be super op for no reason, cause getting up to a hill would be super difficult but once there you would be nearly untouchable...And if the above is false it would be the other way around, cause getting up to a hill would be super long but once there the newcomers would have a easier way since they could just attack you 1 turn sooner and they could exploit the new movement (which is way i dont thinkg this is the case).
Well, hills are a good defensive position. And in game play terms, if you got problems with a unit on a hill, just get ranged units to shoot it down?

I think this will make combat much more interesting (though I do see the AI having problems with that. D: )