In Europe, prior to the rise of modern road systems, probably 40% of the saddle stock performed an "ambling gait." Some were quite typey, some were just "fortuitous accidents." These horses were valued in a time when roads were poor and if you had to travel by land it was in a wheeled vehicle (without springs or shocks on a bad road), astride, or via "shank's mare" (walking).
One of the roots of modern dressage was the need to take ambling stock and make it more compatible with trotting horses for military use.
In the Americas, prior to the development of modern road system after the ACW, the ambling horse was very valuable. As it was in the Carribean and Central and South America. It's value declined as road systems got better and as rail systems became the primary "people movers."
We North Americans often forget that there are entire horse cultures South of us that parallel, but don't precisely match, our economic and cultural development. This includes the development of several types of ambling horses.
As I noted before, if you're going to try for a new type leading to a new breed then intelligent cross-breeding and intelligent selection of production and get for future breeding is not a problem. "Back yard breeding" without critical thought doesn't produce new types, it produces meat horses.