I think I understand the "getting horses right" issue. It's not just a matter of movement, but giving them combat characteristics, and armor, too? The lack of mounted combat in the Eldar Scrolls games was extremely frustrating and disappointing. The issue was only recently remedied.
With no fast travel, and if there were no mounts, but perhaps caravans, would we be able to fast travel by paying for a ride with a caravan, or other group? The way I see it is, if you are alone then you need to be constantly vigilant, but if you are with a large group then you can afford not to pay as much attention, thus the game follows suit and ignores the travel time. On the same note, as with the original two Fallout travel systems, there could be a chance for hitting random encounters, as determined by what you would actually encounter normally.
Alternatively, what about forming a group which we lead, in which case we don't get a fast-travel time-skip, but we do get payed?
I also had a silly idea for if mounts get in: could there be a bike? Not a modern bike, not even one of those huge wheel ones, but a single example of the first bike.
You can see it's a steerable push bike, and it was invented by a baron, in 1817, as a replacement for horses, capable of 9 mph. One site, says it was so he could get around the royal gardens faster. Another says he based the design on a similar, but unsteerable precursor, the celerifere. A similar scenario could exist in the game, and opportunity could present itself, or be made by the player, to receive the bike.
http://en.wikipedia.org/wiki/History_of_the_bicycle
http://www.pedalinghistory.com/PHhistory.html
http://inventors.about.com/od/bstartinventions/a/History-Of-The-Bicycle.htm
http://en.wikipedia.org/wiki/Karl_Drais