There are a number of SKINs associated with various NPC corps, such as Kaalakiota and Wiyrkomi. They were shorter runs, and have yet to be cycled. What would give them a way to make a comeback is to add them to loyalty point stores for their respective corporations.
To keep their value from plummeting for the hodlers, it wouldn’t be a terrible idea to make them require more than a trifle to purchase … just pulling random numbers from thin air, 100K LP and 200M Isk for a BS-class skin would still keep them with quite a bit of value.
Someone looking for a specific currently-unavailable SKIN could obtain one with a bit of work. Someone intent on collecting them all would be forced to spend tremendous amounts of time, LP, and Isk to obtain every one running missions for many corporations.