Like will I be able to order it after it releases and still get the Diablo wings and card back?
Most likely. You can still upgrade old xpacs to collectors editions for wow so I don't see them changing it. It's extra money after all.
Looking at the MoP digital deluxe edition that was up until just before WoD hit iirc. So I would assume that Overwatch's origins edition will be in stores and available on Blizz's store to purchase for a while after it releases.