This has long been on the wishlist of many Fallout fans, that considering how many broken down and dilapidated vehicles you find around the world, you can't drive even a single one of them. It doesn't really make much sense that you can't find one in suitable condition to drive, and it'd add a whole new dimension to the post-apocalyptic experience. Now, on one hand, it would completely change the game and require a massive mechanical overhaul from Bethesda, but if they paid due attention, it could open the series up in brilliant ways. Perhaps a fuel limitation mechanic similar to the Power Armour's Fusion Cores would prevent it from being over-powered, though the fact that most of the series' big confrontations take place indoors is itself an easy way to prevent vehicles from making things too easy. Yes, a lot of the fun in Fallout 4 is venturing across the seemingly endless wasteland and vehicles would probably make the world feel a lot smaller, but it'd also be super-fun to mow down raiders Mad Max-style, especially if you could customise your motor of choice.