Back in 2008, Mark Frauenfelder broached the miniature cattle topic, and a recent post on reddit brought it back to the fore, warranting an update for when you're only a little bit ready to get a cow.
Expanding on top of the miniature Dexter cow breed in Mark's 2008 article, Rural Living Today has this miniature cattle breed compendium:
Oddly enough, there was no mention of a mini-Wagyu lineage, but were I part of that marketing team, I'd argue for dropping the hyphen, and mashing all the letters together in lower case like this: minikobe™, "For Fatted calf times, make it minikobe™ beef time."