Blizzard have made an announcement regarding the physical Collectors Edition, which is especially relevant to anyone who wants to buy/has already bought the digital version:
Upgrading from Standard or Digital Deluxe to Collector’s Edition
If you’ve purchased a digital copy of Battle for Azeroth, but want to upgrade to the Collector’s Edition, we will automatically credit you the cost of the digital copy in Blizzard Balance - as long as you enter the Collector’s Edition key before 11:59pm PST on December 31, 2018. When you enter the key from your Collector’s Edition, we will see the original transaction on your account and the credit will kick in. Remember, you will need to enter the Collector’s Edition key before the end of the year, as automatic Blizzard Balance credits will be turned off at 11:59pm PST on December 31, 2018.
Please note, if you bought a standard edition then upgraded to a digital deluxe, you will be credited for the original copy only.
Standard Digital / Digital Deluxe > Collector’s Edition
If you bought the Standard OR Digital Deluxe copy of Battle for Azeroth and pre-ordered the Collector’s Edition, your Blizzard Balance credit will be the price you paid for the original copy.
Standard Digital > Digital Deluxe > Collector’s Edition
If you bought the Standard digital copy, upgraded to Digital Deluxe at a later date, then pre-ordered the Collector’s Edition of Battle for Azeroth, your Blizzard Balance credit will be the price you paid for the original Standard Edition.
Which sounds much better than previous ways they've handled digital v physical versions.
Included in the Collectors Edition is:
Double-Sided Story Book: Elegy & A Good War
Every great war story has two sides. This limited edition hardback version collects two new World of Warcraft novellas depicting the Burning of Teldrassil from the point of view of the Alliance (Elegy, by Christie Golden) and the Horde (A Good War, by Robert Brooks). Each story includes original artwork exclusive to this edition*.
Horde & Alliance Double-Sided Mark of Allegiance
Declare your allegiance with this hefty, double-sided Mark of Allegiance. Place it somewhere prominent, with your chosen faction proudly facing out into the world for all to see. Includes stand.
Collector’s Edition Digital Soundtrack
A digital key to download the stirring orchestral pieces from the Battle for Azeroth soundtrack, the perfect mood music for laying siege to your enemies.
World of Warcraft: Battle for Azeroth PC/Mac Game Key
Digital key to unlock the full version of Battle for Azeroth.
Epic In-Game Content
Unlock a treasure trove of Horde- and Alliance-themed in-game content within World of Warcraft and across other Blizzard games:
World of Warcraft
- Gilded Ravasaur Horde Mount
- Seabraid Stallion Alliance Mount
- Tottle, The Baby Tortollan Pet
- Character Boost to Level 110
- Azeroth is Burning Card Back
Heroes of the Storm
- Primal Flamesaber Mount
- Tracer Alliance Banner & Horde Banner Emotes
- Torbjorn For the Alliance & For the Horde Emotes
- Zandalar & Kul’Tiras Icons
- Anduin, Jaina, Sylvanas and Varok Sprays
- Alliance & Horde Sprays
*Both stories will become available online later this year, but buying the Collector’s Edition will remain the only way to own the exclusive hardback version containing original artwork.