So, its occured to me that it would be a massively fun event if we had a day or two where you had to ride or run everywhere, and use the boats between alliance area and DLC areas.

Its possible to go everywhere in game without actually using a wayshrine. The rules of the event would essentially say that all magical travel was somehow being suppressed, so it wouldn't even be possible to insta-travel and pay the small fee.

Even all trials actually have a front door you can use, its just a case of knowing where they are. (MoL in Reaper's March, AA, SO and Hel Ra are in Craglorn). To get to craglorn there is either the travel carts in the capitals or the gates in Bangkorai.

You could even apply it to Cyrodiil, whereby the transitus network has ceased working, and thus make the PvP much more challenging.