I'm sorry, but it seems to me a lot of your theory hinges on subconscious!Harry wearing the duster before the duster makes an appearance. Doesn't the new coat, the one that is definitely not the black leather duster, mean that the future!Harry you say is subconscious!Harry comes from before Cold days?
Hence the phrase that seems to be more important that any other... "
No matter where you go, there you are." Somewhere in this series (I forget where) there is a conversation between Harry and someone else where it's stated that linear time really doesn't exist, but that's how a mortal's mind perceives time. It could have been Uriel, or maybe Leanansidhe. I think it was in
Ghost Story. Einstein would agree since he spent his last few years as a scientist stating that past, present and future all exist simultaneously. They are a single existence.
In other words... "
No matter where you go, there you are."