With a more condensed overworld, I don't see any reason to use Epona, even if one could. Even if it's bigger, there will be more in it and you won't want to speed past anything. Hyrule Field was the only thing Epona was good for, and they implied that there will be no such expanse in this game. There are other ways of jumping fences.
When long-distance travel is necessary, Link could use his Skyward Sword as "his driving force behind his traveling between lands." And I don't mean that it would allow him to fly to other locations. That would be more silly than moving solid stone blocks five times your size. They say it allows him to travel between Sky Loft and the land below. I can see Sky Loft acting as hub in much the same way as Relto
contains linking books to most of the ages in Uru
. Use the SS to go to SL, then use it again in a different area of SL (which would be much smaller than the overworld map) to go to the surface in a different area.
As much fun as it would be, no Epona, and no flying please.