How does pre-purchase and Collector's edition work?

[Perl-anetheron (Perl)]

A few days after you originally posted this, they announced how they would handle it officially

Upgrading Your Version of Shadowlands

To answer some questions in regards to the Collector’s Edition and its content: In the coming months, we will announce our retail-only Collector’s Edition to commemorate the release of Shadowlands, featuring everything in the Epic Edition, and more! – We have seen some questions about how upgrades will work for the different versions of Shadowlands. While the process is similar to the last expansion, we want to take a moment to clarify how upgrades will work for some of the most common situat…