Is it possible to make these a short cut instead of an item, similar to the mod "Wire Shortcuts?" In relation to this suggestion, if you can get these to work from the short cut bar, possible have a drop down to be able to select the specific vehicle so that you can call multiple different vehicles?

Seconded this request! Also the multiple vehicles dropdown!

Is it possible to make these a short cut instead of an item, similar to the mod "Wire Shortcuts?"

I think I've figured this out. Should be possible to migrate everything to a shortcut.

In relation to this suggestion, if you can get these to work from the short cut bar, possible have a drop down to be able to select the specific vehicle so that you can call multiple different vehicles?

Nope, calling multiple vehicles isn't anything I'm ready for yet. You click on the ground and the one vehicle you own will come to your. However, I imagine that selecting multiple vehicles would open a GUI giving you stats about the vehicles and allow you to claim a vehicle (giving up the old one), lock your current vehicle, or unlock any number of vehicles you've locked. There could also be an option to reclaim ownership of one of your locked vehicles if your current vehicle is destroyed or stolen by another player.

Added for 1.1.2 (will be released when Vehicle Wagons is updated with some minor compatibility patches): The keys are no longer an item that can be crafted, but a shortcut (which still needs to be unlocked by research). You can use the keys as before (click on vehicles to claim/lock/unlock them, or on the ground to summon the vehicle you've claimed), or select an area to get a GUI showing all eligible vehicles within that area. You may use the GUI to claim a vehicle you've locked, or to toggle the lock of vehicles you've claimed/locked. You may also use it to assign a custom name to vehicles you've claimed/locked, or to unclaimed/unlocked vehicles that have no custom name yet.