As for your game. Having the character in just two forms is somewhat of a limitation, but then any more and perhaps it would get too confusing. I like your suggestions for how this bi-ego would challenge the Player’s sense of unique/complete-identity. In addition to what you’ve said, the NPCs could be perceived differently depending on which ego is being played at that moment.

Another thing which appeared in the book which would be nice to conceive in the game, was distances appearing to change. E.g. the distance to the bridge.

Great ideas on how the game could break out of itself!

I like the idea of adding ARG elements. I thought it worked VERY well in In Memoriam (aka Missing).

But I still don’t quite get how the game would work? What would you first see when you start it up? What is the first task? How will the player know what to do? When does the perspective switch to the other character?

Also, you described how a journal in the book seems to have passages from the book itself – how would that work if the game?