yes man, yes. I dream of a game like this.
The problem of having an open world is that you can no longer have puzzles that consist in using objects in uncommon ways (mcGyver style). Because in an open world there would be more logical substitutes for those objects. An interesting question is how many puzzles in TWP you would lose. Another interesting question is what are the kinds of puzzles that would survive. (I remember Ultima 7 had subsections where you are locked up in dungeons, or in alternate dimensions, with few objects in the inventory, exactly because of this problem.)