I hope no-one minds me resurrecting this thread, but beefing up the various Central Asia / Steppe Nomad empires is something I've wanted to see for a long time, but have lacked the skill/knowledge (and time) to do it myself, so I'll share some of my own thoughts on what could be done.
First off, I think that regardless of how it’s done, something definitely does need to be done to power up the various steppe peoples. While they haven't produced many great civilizations, they have certainly been influential on (and often extremely dangerous to) their settled neighbours in Europe, China, Greater Iran, and even India.
In the East, they are reasonably well represented: the Xiongnu/Hsiung-nu (the "Mongolian" nomads who spawn in the Classical era and harry China) are a significant threat that require a substantial investment by the Chinese to keep them out, and if you're careless can easily take a city and deny you your UHV. (Although they don't appear early enough to stop me sending my starting warrior marching across Eurasia to pick up all the goody huts from Mongolia to Spain, which just should not be possible).
But in the West, apart from the Migration-Era barb spawns, they are seriously under-represented. The Ancient/Classical-era steppe peoples such as the Scythians and Sarmatians get only a few barbarians who can't do much to stop you settling there if you really want to (in a recent Greek game, I founded Kazan and Stalingrad).
Historically, the early Rus states fought long campaigns against third steppe neighbours, and only beat them in time to get WTFPWNd by the Mongols. And even after they threw off the Mongol Yoke, they suffered continued harassment by various successor Khanates (Golden Horde, Crimean Tartars, etc). But in the game, they just get harried by a few horse archers who can easily be fought off, and of course the Mongols are quite frankly a joke.
So what to do?
I've had several ideas, of varying complexity.
The simplest way would just be to add more barbarians and independents, both units and a few cities. I would suggest an independent, Jewish city spawning in the North Caucuses (and possibly a few other cities in the surrounding area) around 550-650 to represent the
Kazars, at least one barbarian city just outside the Russian flip area spawning at the same time as the Russians or earlier, possibly a barbarian city in Mongolia before the main Xiongnu spawn to make early Chinese exploration a bit harder, and a few other barb/independent cities in Siberia and Central Asia so that the Russians actually have to fight their way to their UHV.
My second, more involved idea, would be to do the above, but rather than (just) using barbs and independents, create a "Steppe Nomad" minor civ (with behaviour similar to the Natives). Possibly
two Nomad civs, one aggressive one like the Natives and one peaceful one like the Independents (to represent the Kazars and other more peaceable steppe peoples). To add a bit of uncertainty, the two should have the same civ colour and flag.
The third, most involved idea, would be to change the Mongols to represent various nomad empires from across history. I would suggest starting in Mongolia around 200BC, to represent the Xiongnu, and with UHV conditions and settler maps designed to represent the conquests of the Huns, the Mongols, and the Timurids. For example:
* Control Central Europe [or raze x Roman-area cities] by 453 AD (the death of Attila)
* Vassalize Russian and China (or conquer their core areas) by 1294 (death of Kublai Khan)
* Control the Persian and Indian core areas by 1405 (death of Timur)
Alternatively, the last UHV could be "still be alive in 1760" (a year after the last steppe empire, the
Zunghar Khanate, was destroyed by the Chinese).
Possible leaderheads:
1) Starting leader: Attila the Hun (very aggressive and raze-happy, but can be bought off with regular tribute).
2) c. 1200: Genghis Khan (aggressive and raze-happy, but willing to accept vassals).
3) c. 1360: Timur. (Very aggressive, raze-happy, and a religious fanatic).
(And yes, I know the theory linking the Huns with the Xiongnu has fallen out of favour, but I don't see the need to add a fourth leader to account for that. Not when Saladin, a Kurd, gets to rule the Arabs for their entire history).
Possible power: "The power of the Steppes: mounted units can be built without access to horses* and don't cost maintainance**".
* To represent the fact that eveyone will take their herds with them.
** To stop them being bankrupted if they end up with lots of units and few or none cities.
This would still require a few independent or barbarian cities in Central Asia and Eastern Europe to hold up both European and "Mongolian" expansion.
In addition to all this, the Turkish spawn could be moved to 11th Century (or maybe earlier) Turkestan, to represent the Seljukes.
