Divine Serpent man only?

I believe it has less to do with balance and more to do with the historical/thematic element.

C'tis should get anything reptile. I also wouldn't feel too bad about Mictlan having access to the DS. I'd hope they would allow every race a higher dominion (3-4) and higher starting magic (3) in at least one field, so that they can more appropriately use some of those blessing effects.