Too many people would whine at there being wait times for travel.
That being said, I'd be all for it if it were a shortened trip. Obviously you would not want to sit there while your horse traverses the entirety of Skyrim. There were airship rides in FFXI that lasted 3 or 4 minutes, and boat rides could get up to 10, which allowed for fishing and random monster pops.
I'd love to see this sort of thing in ESO, but the whiney MMO kiddies would do nothing but complain about it. Everything must be NOW NOW NOW these days.