I briefly lobbied for this in Spintires, so here I am trying again.
Would like to see hold bindings (as opposed to toggle) for things such as hand brake, all wheel drive and diff lock. (maybe something else?) This will allow me to use flip switches for things you'll generally use for more than a few moments.
This could be implemented in the binding UI with a checkbox next to the binding, which you would check to get the hold functionality.