Why would you want a horizontal tracker interface?
I mean like Saga said, Famistudio isn't a "horizontal tracker interface". If I were to express my real honest opinion, there's no such thing as vertical or horizontal trackers. They're just trackers.
Sure I see what you mean with a "horizontal" tracker interface, and it technically would work. Thing is, all other trackers have been made the other way due to a normal standard and being kept so for the sake of human direction sense, so why would anyone want an interface that completely swaps directions?
It will just disadvantageous mess with the sense of direction when you switch or use multiple trackers - I think that is why nobody has made any "horizontal" trackers.