At one stage TGC were talking about a feature that was going to be included to restrict player movement at the edge of the world or whatever.
Personally I think that something like a Zone feature with points or whatever that can be manipulated, added, shaped and so on could be used both to prevent players accessing areas of a level and also similarly to restrict enemies or other types of characters to areas you want to keep them in or exclude them from - so they can patrol, attack or walk about (including civilians) and do whatever business you have them doing where you wish them to be and stay in such instances thats needed. Such would be very flexible in Game Making scenarios to make much more impressive games with a lot of possibilities. I had suggested and requested this a few times previously but no headway on anything like this as yet.....
So yes a simple way to prevent access to the edge of the level for the player at least would be helpful preferably not needing to be rigidly square or rectangular around the exact boundary edge or perimeter as that's a bit naff as the player should not really be allowed to get to the exact edge of the world and see theres nothing there ever - and something that does not need take up too much resources as its not a visual game feature that's needed in that way.
Ideally of course the previous suggestion where boundary or zones could be set up to restrict/control both player and enemy/civilian Characters to specific multiple areas in a level would be far better for game making would be even better as an invisible boundary extent zone alone to just stop the player falling off the edge as it were does little to actually improve the games you make and make gameplay much more flexible and exciting as the other extended suggestion would.
Anyway I guess the Player boundary things would be the easiest thing for Lee to do if it could done without impacting performance. Any other more advanced or complex Zone suggestions are likely to not get very far at this stage at least for certain I should think due to so many basic things missing yet to hopefully be added.
Still we can keep asking so things can be considered lest they fall by the wayside.