I see where you are coming from, but highways and public transit are completely different animals. Subway tracks take up less space than motorways, and are quieter/have a greener footprint than a motorway. Elevated transit systems continue to be built in cities like Vancouver, and considering NYC's history with elevated transit, I do not foresee much of an issue. Public transit coming back to the area would not only act as a revival but would be greatly appreciated by those who only have to access to buses with depressingly low average speeds. Plus, would be more willing to build elevated due to it's cost advantage over boring a new tunnel (return on investment).
If they do go for an EL (that is the Bronx extension gets built at all) I would like to see concrete viaducts or something more modern like the AirTrain rather than the antiquated design of the current El's