Zebra 9
Emperor
I have also created a MOD COMP that allows this (should make an update for it).
We will start working on quantified resources once BtS comes out and Dom finishes his other mods he's currently working on.
As a follow up on your idea, instead of having specific breeds to work with (which would entail more resources), you could simulate this using a promotion. You can set a specific building, like the Arabian stable in your example, to give a unique promotion, e.g. Arabian Horse, which might give combat bonuses and/or +X % against a unit type.
The result should be that roads and rivers are key for trade until the classical era, where sea becomes dominant. Here, medium distance trades should the most viable: Trade routes from Rome to China should be rare (if basically non-existent, save a Great Merchant pulling a big mission), but trade with Persia might be quite profitable. By the renaissance era, ocean trade should be viable, but only across a single water mass. Only with the advent of combustion should the ideal trade take place halfway around the globe.