Just to add my voice to this discussion. I bought the DAI Deluxe Edition, and it's crazy that there is no upgrade path to the GOTY edition. My only options, it seems, are to either buy all the DLC separately or buy the game a second time.
You offered a Standard Edition to Deluxe Edition upgrade, so why is there no Deluxe Edition to GOTY Edition upgrade?
What's particularly insulting about this situation is that someone buying the game today can pick up the whole GOTY Edition package for £29.99 whereas people like me who bought the Deluxe Edition on release for £64.99 must, even now, pay an additional (11.99+11.99+3.99+3.99+11.99=) £43.95 to get the same content.
My cheapest upgrade option is £29.99, i.e. buying the game a second time in GOTY Edition form. That is crazy.
With these kinds of practices all you are doing is punishing and insulting the people who paid full-price to buy your game on release. You are sending a clear message that buying your games on release is a foolish choice, and the wise choice is to just wait for the GOTY Edition. Is that really the message that you want to be sending?