Personally, I really like lucky nations because it gives you a challenge in the lategame.
There is a lucky nations off setting iirc
Concerning the precise buffs, I would wish to make a distinction between buffs for the Steppes and Buffs or Asian nations.
First: Steppe buffs:
-Historically, Hordes differed a lot in terms of sedentarity etc. Kazans capital was a pretty big well fortified city, while other Khanates were actually quite different.
This could be implemented using a slider (akin to piety for Muslims, or Patriach authority for Orthodox), that is moved by events and shows how sedentary/nomadic the tribes are. Being nomads means considerably more manpower/discipline/morale , being sedentary opens the way for gouvermental and technological reform and increases your strength in the long term.
-Hordes should definitly get new units. Kazan did make considerable use of pistols, and of cannons (typcially, artillery troops were Ottoman trained though, keeping a cannon working in battlefield conditions requires different skills from using them in battle), the problem with getting modern regiments for the hordes was their failure to develop manufactoring centers for weaponry, Ottoman largesse got them only so far, although the difference between a Horde being backed by the high porte (Crimea survived quite long) and hordes that werent (Sibir fell really easy, Kazan/Nogai put up quite a fight) was quite significant irl.
Ways to profit from more advanced neighbours that arent westerners would be a pretty smart and historic way to do.
As far as Asians are concerned: Simply buff their military units, its ok for them to research slowly, but the huge power differentials in the mid game are unhistoric. Portugal lost a number of engagements at land (they dominated at sea though), and Britain began to conquer at the end of the time period, not in the 16th century.