I love the flavor text and especially the paragon paths a lot. The Thoughtful Displacement Power seem excessively complicated and I'm not big enough on the numbers to know how skill checks balance versus attacks but it seems both fun and extremely useful. I'm not sure I like attaching a role requirement to a paragon path, though. The RAW already prevents non-rangers from taking ranger paragon paths and I'm enoying playing around with characters who mix roles. While a yuan-ti fighter or warlord wouldn't get the maximum benefit from the Serpent Blade Dancer I certainly wouldn't want to restrict their ability to do so (I could definitely see the Master of the Scimitar trait opening things up for a Fighter in terms of his weapon type-specific powers.)
I'm torn on the racial power. I would make the power a move action (with a feat to make it a minor.) At first I thought the poison attack was a little overpowered, but when you take into account the fact that you need to make an extra attack roll for the poison to even take effect (and Deathjump Spider Venom's paltry +8 isn't going to be very effective towards the later levels of Heroic tier) it seems to balance out fine. Lasting Virulence on a Yuan-ti Orb Wizard might a broken combo, though.
Overall I really love it, and I definitely want to make at least the paragon paths available to my yuan-ti players.