If you try to set aside a highway via inheritance you are going to have a bad time. Your estates will just be cantrips, leaving the cost of cards completely unaffected. Why, you ask? Well it is due to the new formulation of the inheritance rules:
Inheritance text: Once per game...During your turns, Estates are also Actions with "Play the card with your estate token, leaving it there".
Highway text: ...while this is in play, cards cost 1 less.
So you play your Estate, which plays your highway, leaving it there - meaning leaving it out of play. This means that the highways text does not take effect as it is never in play as is required to affect cost.
This happened to me and my opponent during a game, both of us assuming we were being very clever, reducing cost so as to use inheritance on a high cost card. It left us puzzling over why our estates weren't doing anything. We assumed it was a bug until we read the text of the two cards very carefully.