Skins Per Year (SpY) Chart
I have a LOT of free time. As you can tell, one of my favorite champions is Taric, and this all started as a way to see just how underloved he seemed to be. Calculating his and a few other champions skins per year (SpY) snowballed into me doing it for every champion! In the link, you will find a doc with the SpY data for every champion as of February 21st, 2016 - League of Legends' birthday. Some other random data is thrown in as well.
Notes: Blood Moon Yasuo & Kennen ARE included. Recently released champions with only one skin are NOT calculated The Average Skin Value is as of this post, a WIP Champions released more recently have much more sporadic changes than older champions, which the reason for my bias below.
Fun Facts from this info:
The champion with the best SpY (released before 2014) is not Ahri, not Miss Fortune, but Gragas... Gragas
The champions with the best SpY (released before 2014) are
The champions with the worst SpY are

It's sad that most champions in the bottom group will almost definitely never get close to the average. A
shed for our forgotten comrades.
I can't wait for the Taric rework. Give my boy some new skins.