I'm expecting a case where someone is a) denied a non-res license for no good reason, by b) a state that does not recognize that non-residents' home state (or other) licenses.
Alternatively, someone could a) apply in a state that has
no non-res license available to them at all and which state b) offers no recognition of a non-resident's home state license (NY technically, IL for residents not on their list of states whose residents can apply for an IL license). That fact set in particular could be based on and reinvigorate the
privileges and immunities clause (the Article IV "comity clause") (rather than be brought as a 14th A. privileges
or immunities clause case, or as a 14th A substantive due process [which Thomas hates the use of] case).