Hi, I have an idea for the community to tell me why it can’t be done. Anyways, here it is.
The idea is for a unique villager for the mongols. What is special about this villager? This villager has 65 hp, and increased movespeed. It moves as fast as a mongol ram that does not have any units garrisoned in it. It also has reduced carrying capacity. It has half the carrying capacity as a normal villager, so even though it can carry stuff faster, it has to make twice as many trips. The exception is that it has triple the normal villagers capacity for carrying food gathered from hunting. Because its not quite double the speed of a normal villager, this unit is in fact worse than a normal villager when compared to normal villagers for all gathering tasks except hunting.
Second, this villager cant construct many buildings. It can only construct yurts, palisade walls, outposts, lumbercamps, mining camps, and mills. It can construct all 8 kinds of yurts though… 
Third, this villager can only be made from castle age onward at the town center.
So, I think this wouldn’t upset the balance, and it would be a niche unit with a specific place. Because it can only be constructed in castle age, its useless for rushing. Because it has less carrying capacity its also useless for gathering when compared to a normal villager. By the time castle age has rolled around, all the animals have been mostly hunted out, and this villager is mostly useless by that time specifically because of that. If animals are left on the map, they are far away from civilization, and that is where this villager has a niche. It can hunt animals far away from the mongol main base and still be cost efficient.
Another niche this villager has is in constructing scouting outposts. In most maps, by the time imperial has rolled around most people have tons of vision. Outposts are rarely constructed, and palisades are not used once stone walls become available. This villagers speed combined with its unique construction set ensures that the mongols keep using palisades and outposts.
The last niche this villager has is keeping up with the mobile mongol army to repair their seige weapons. From a gameplay perspective, this is the ability I think is probably the most impactful to gameplay.
Thoughts?