I’ve been refraining from doing this topic, but since a lot of people is giving their opinions about balance changes, I’m gonna give mine. I’m gonna divide this into things I think should be changed, and think that, while not necessary, could be changed to make some civs work differently.
Here we go:
Thing I think need to be changed
General: Steppe Lancer needs some rework. I don’t have a super clear idea for this, so I would include it in the other section
Burmese: Nerf Arambai, either reduncing the attack to 15, or Reducing the range to 4. They’re to OP, specially in castle age. Other option could be nerf the creation time to 23 or 24 seconds
Italians: Free archer armor techs. I originally tought this idea for Koreans, (and still could apply for them) but could be viable for italians as well. Other option is that Archer line upgrade cost 50% cheaper Also GC creation time could be reduced to 21/18 or even 20/18
Indians They’re too strong in pocket position. They eco allows them to boom 3tc and make tons of camels at the same time. I would reduce the vil bonus to 10/15/15/20 Elephants archers range should be increased to 6 in order to make them have an advantage againts regular archers (plus… they’re shooting from like 5 metters high, you know…)
Khmer: Either take away Heavy plow, or even Hand cart (yes, heavy nerf, but overall needed). Yes, other option could be nerf their elephants (Take away the speed bonus or nerf tusk swords) but, even with weaker elephants, the infinite spam would still be to much. Khmer are still broken, even after the last nerf to elephants. For me, the problem is not the elephant itself, but their insane economy. It’s senseless to have the best food economy and the best unit in pop efficience in the same civ (unit that cost a lot of food). Instead of nerfing their elephants further more, I would nerf their economy
Koreans: Free archer armor techs as I say, this could apply either for koreans or Italians. Free elite skirm is another option. As @horapallas said Panokseon should not exist. Turtle ships should be granted for free (or maybe in the elite) and the tech dould be replaced for +2 range for towers (extra range bonus dissappear, becoming, thus, this UT)
Portuguese: Skirmishers and spearmen have +10%/15%/20% HP in Feudal/Castle/imperial OR Skirmishers and pikes have +1 range (should lose Halbs if this idea is implemented, altough eveny Pike +1range could still be OP) Ports are amazing in water, and awful in land. While their gold discount isn’t bad, it feels super generic. Trying to keep this “jack of all trades” identity for they military bonus, I came with the idea of buffing their trash, making it superior ir some way. Arquebus tech should be fixed. Also Portuguese could get Squires.
Turks: I have several options for this one. For me, the main issue for turks is their problem to handle archers in the long rung (HCA being the only option they have in the long run). So I have several Ideas. The first, more discussed and controvertial: Give them elite skrims I consider elite skirm a basic unit for 1v1 that can’t be replaced with anything else (while halbs role can be covered with camels, for example). Other option could be give them a semitrash infantry unit that counters archers and halbs some infantry costing arround 50F and 10 gold. With 60hp, 7 attack, good speed, high PA, and bonus attack againts archers and halbs, but no Melee armor (could be named YAYA, as the iregular ottoman infantry corp). giving Hussars +3damage againts archers coud be another option, altought this would make turks even more a one-trick horse, I mean pony 
last, but not least, a grenadier could be added as as second UU. Like the slinger, but with an slower fire rate, and a small blast radious, could be useful to attack group of archers (maybe give it +1 or +2 againts archers). If either the Yaya or the grenadier are added, they should be an Imperial Age Unit (first from the barracks, second from the archery range)
Changes that could be interesting to try out but I’m not sure of:
General: Steppe Lancer need to find a niche. I guess the best for them is to become an anty infantry unit: So I would rework it like 70F 30G 8/10 attack for non elite/elite, with +8/+10 againts infantry and +3/+5 cavalry class armor. Something like a weaker cataphract, in order to make them viable to mix in with heavy cavalry. A costly adittion that can make the army much more powerfull. I would nerf other stats (armor, HP) in order to make them more vulnerable to knights and archers
Berbers: Explosive ships +33% damage OR +33% blast radious Berbers are supposed to be good in water, but their bonus is highly neglectable. This could work fine with their faster ships bonus
Burmese: If arambai are nerfed, they should need something for their castle age. Skirms +1PA per age starting in castle age since Howda was nerfed, arambai became the only answer to archers. Also burmese elephants should get a buff, in order to became a viable unit for them (supposedly they are an elephany civ) Elephants have 200% trample damage (basically, it reverse the last nerf for burmese)
Indians: Sultans could hipotetically unlock battle elephants for indians (only if their eco is nerfed)
Lithuanians: as some well-known user stated some time ago, Leitis concept is weird, since it’s supposed to be a better version of the best paladin available. A wild idea would be, as he o someone else proposed, to make it a glass cannon. I came with an sketch of it in AOEzone some time ago: stats similart to:
60F 30G (non elite/elite stats)
attack: 15/18
HP: 50/70
MA: 0/0
PA: 0/1
Speed: 1.5
Training time: 10/9 seconds
not precise numbers, but that’s the idea. Good for raiding and last minute defense for your castles. ideal for snipping trebs
Saracens: So, Saracens are a bit odd civ. They were supposed to represent all muslim civs, and thus, where made good at every field. Currently, they’re used as an archer civ, altought they’re supposed to be a camel civ. Plus, their team bonus can be a little OP with certain civs. So I though this: replace the team bonus with the concept of Madrasah. New team bonus: Monks retuns 20% gold cost when they die. And replace Madrash with a new UT for castle age: Damascus Steel (300F 200G): Camels have +2 attack At the end, saracens camels would have same attack and +10Hp than indian camels, but less PA, slower creation time and no bonus againt’s buildings (and no eco bonus like Indians do). It this is to much, zealotry could be modified to give only 20hp to camels and mameluks (and adjusting elite mameluk by giving it extra 10hp)
Anyway, I guess those are a lot of Ideas. I hope some of them might be useful. And if not, well, it’s always fun to play arround balance ideas.
EDIT: I forgot to add, that, if buff to elephants is to strong for burmese, anoter way I found to buff them indirectly is giving Burmese Free faith.