I'd question your ability to read but I think I should show greater concern in the fact that you stated two completely different things in two sentences.
I never said that Yoshida "can't" implement it (if you can quote me on that you will impress me greatly). I said it would be a waste to implement it. To implement something takes a great deal of money and time. So you have a fiscal cost and a time cost. A good way to sum up both is to use the term 
"opportunity cost". Since it requires labour and time to create such a thing (this idea is irrelevant to the engine currently in place in the game so the idea would have to be newly implemented), you would need to consider the fact that they'd be wasting time/money developing this new system when they could be focusing on more important things. The game isn't even out yet, it's only a few months away from being released.
Yoshida doesn't have this magical infinite team of wizards that can do everything and everything and only have "time" to worry about. There's only a certain amount of people to each particular department and it takes a lot of production cost (time and money) to implement new ideas. It is ridiculous that I even have to explain such a thing in such a thread. I shouldn't have to. It should be common sense.
People need to get rid of the idea that making games is some easy task and that any idea thrown at them in big enough of a quantity should be implemented. Is it possible? Yes. Would it be productive? Not at all.
If you have ideas for mounts, simple ideas, go for it. What's with all this silly stuff like turn radius and acceleration? Here's a better idea for people who support this sort of thing. Create an outline on all of the positives and negatives this sort of system would have. Why would people want this system? Why would the game be any less enjoyable without this system?
I see silly comments like "playing dress up" (from someone from Balmung, the RP server dominated by roleplayers) in some sort of patronizing way as if there is something wrong with that style of play, even though that's the style of play that seems to be favoured by not only the majority of players but the development team itself.