Joining you now.
Just finished the article Ambiguous Cad, I think I will look around for more. As an anthropologist, reading about the economy and culture of ponies is quite entertaining.
The system looks similar to the Varna system; Unicorns would definitely seem to be the Brahmin, earth ponies the Vaishya, pegasi the Shudra, however the stratification is different in the ponyna system, the pegasi seem to have higher rank than the earth ponies.
Cutie marks seem to determine what Jati the individual belongs to, however it is interesting that they don't get their cutie marks until later in life, which shows that there is some fluidity - which mirrors the relationship between Varna and Jati caste systems.
Zebras would be part of the scheduled castes, I imagine that is where other non-pony, non dragon entities would also be placed.
Luna and Celestia would be the only two known of the Kshatriya.
By working together with the magic of friendship, the other castes were able to have an uprising against Luna, but that ability was wielded/lead by a member of the Unicorns, the priestly class
Just a thought.