Okay, so Yoshi has tentatively put forward 3 possible limited edition 1 time only mounts. He's even said he's not sure about using those three, so it's clear that he's being selective and careful about what he chooses to be a mount. Considering this, he's not going to just start making anything and everything mounts willy nilly, nor will we have hundreds of mounts, so I don't understand how people are getting this.

People are taking this tentative look at a few distinct mounts and translating it as "omg I don't want hundreds of mounts I can't believe he's doing this." That's drastically jumping to conclusions. Yoshi's smarter than this, and it's clear from the live letter alone that he's considering mounts carefully.

In short, don't argue extremely unlikely and far off scenarios to try and make your case. It's not WoW, it's Final Fantasy.