Running both maps?

[CodeMage]

@WhiteRabbit

It is entirely misleading to consumers to advertise the “new content” as being part of the old game when it’s actually a new game if it doesn’t coexist or interact in real time gameplay with the original product.

It has just recently been confirmed that the expansion pack does add new content to the base game:

You don't like veterans?

Hey there, The Exiled lands will still be available for those who choose to stay in them. Most of the additional DLC content included in Siptah will also be available in the Exiled lands, including building sets, armors and weapons so there is value in the expansion for those who do not wish to partake in the adventures found in Siptah. The base game will also receive normal patches and updates like it did before. Moving to Siptah is not mandatory for those who choose not to. For more details…

So if you buy the expansion pack, you can also craft at least some of the building sets, armor and weapons from it in the base game, too.