First of all, I want to thank you. You are the first one that I see bringing reasonable seeming arguments regarding nagas' tail and not just mentioning how they make things impossible due to magical unspoken reasons and because of how texture wraps around them.
If I understand correctly your argument, you think that with the way that blizzard might be working their animations, the proposed riding animation would require the models' skeletons to have X extra bones for the tail to move properly, correct? I must admit I never cared too much for mount animations and therefore I might not even have noticed if this has changed with WOD, but wouldn't the mounting "animation" just be a static pose? If so, what would be so special about the Naga in particular that would require some ridiculous amount of bones? wouldn't it in a way be comparable to male Draenei tails wrapping around their body while mounting?