- One, which I implemented in Desert Adventure, is to have the boundary be one where the player realizes they will die if they go past the "edge" of the map. Basically, I have a "lost in desert" location where all the exits take the player back to the start location, with the message "Lost in the desert, I walk towards the oasis, the only landmark I can see." seen when they travel from this location.
- Another is to not have a boundary at all. How is this done? With a random map generator. Basically, have the computer generate interesting scenery which extends forever no matter what direction the player goes. The problem with this approach is that there is a limit to the kinds of maps random map generators can make. Basically, a random map generator can make a reasonable approximation of natural scenery, or maze-like maps. Also, a computer can't make the kinds of clever puzzles that are the hallmark of most kinds of interactive fiction.
What a random map generator can generate are "hack and slash" maps; they can work when the objective is to, for example, kill monsters and collect treasures. Random map generators can also make basic "find the key" puzzles; and possibly even "examine things to find stuff" puzzles, but nothing really more complicated than that.
I can see something like this for a role playing game, where the player has skills and hit points, and has the objective of killing monsters in order to acquire more skills and hit points, which allow them to kill even nastier monsters.
However, I am not sure whether this kind of game will appeal to many interactive fiction players. It's a different game, and we knew this as far back as 1981 (Such as Scott Adams' "If you like to kill monsters play 'MACES & MAGIC'!" comment in Savage Island).
Anyway, some food for thought for game designers.