ScottMcPwn
Huscarl
I'm too lazy to look it up, but in the 1304701385701385 post thread about new civs, I posted a list of Silk Road civs I considered possible.
Out of all those possibilities, the ones I consider most likely would be the Timurids, followed by the long-shots in the form of the Khazars and Kushans (who have been mentioned by fans several times in other places). Other long-shot possibilities I considered were the Seljuks, Gokturks, Khitan, Uighurs... that's all I remember. Others I've considered since then would be the Sogdians, Parthians, some sort of Afghanistan civ (but focusing on an earlier history of Afghanistan, like the Durrani or Ghaznavids or something) But of those I'd say the Timurids have the best chance, if only because of Tamerlane.
I would generally prefer a Civ that has survived through out the ages so I would think Afghanistan would be most suitable.