I believe that the reason one has to wait a year to do temple work for the dead is: They are being preached to in the spirit world. When the year is up the deceased have enough knowledge to either reject or accept their temple work. What is your take on this?
My take is that very little has been revealed about the work that goes on in the spirit world. As Latter-day Saints, we have graciously been given the vision of the salvation for the dead and a few non-canonical glimpses into that world. The year wait policy may be driven by some revelation that our seers are privy to of which I know nothing. Or it may also be driven by our consideration for the family members of the deceased. Given the height of emotions that inevitably follow the death of a loved one, it is generally recommended to wait a year before following through with any major decisions – moving, changing jobs, etc. The official policy takes into consideration the feelings of the nearest relatives, so I suspect that the year wait serves to prevent family schisms over ordinances that should yield the opposite.
But that’s just my take on it. The real answer is I don’t know any doctrine on why there should be a year interim, and you and I are just speculating beyond our expertise.