Let's see what do imagine when you think about something Class-Exclusive.
A class mount? Maybe an armor set? A Weapon? Class-exclusive quests? Another exclusive thing can be a Profession. Why not the whole UI to be exclusive for the class?
We are eager to see how you imagine the looks of something exclusive to the Ranger class!
I will suggest an armor "style", I like TESO crafting system because each race has his own armor style, and a lot of other ones that were implemented over the years, but initially there were no more than 14 styles if I can remember well, that you can learn if you find the entire book or separate pages for every piece (hands, head, etc) Anyway there are no "class" styles in TESO but I played a MMORPG, a little one, and I loved that there were armor class styles, was the thing that made me play that one and TESO, and the lore, so yes you can implement something similar to TESO crafting system including that class armor styles that need you to demonstrate your mastery with the class, you can include class ranks and class XP.
So to unlock the head Ranger style you need to be rank 7/10 with your Ranger, or ranger specialization.
Damn you can include a different style for each class specialization.
It looks like this, more class rank is needed for the best class style, that's the warrior helmet, my character is wearing the whole berserker set