Hmmmm A nice suggestion. I was going to place the setting in Shepard's subconscious which is actually a vast desert with nothing but sand. He actually doesn't see Tali till the end. She is actually there witnessing the exchanges between Shepard and the Leviathan but she is both invisible and mute. Its not till the end of there conversation that the Leviathan mentions that "Another has been given our Trust besides you" Then she appears briefly before Shepard is thrown out of his coma.
Like I said it would only work if shepard's mind was at peace. Your desert idea gives a sence of isolation &despair.
Thats how he is. He has no memory of destroying the Reapers. His last memory is pulling himself into the conduit. The Leviathans will explain everything. Shepards mind will be at peace only when everything is right with the world. Tali will be his anchor as well as his surviving squadmates. They bring him some peace but not entirely. Shepards mind is full of repressed sadness mostly from years ago.