When this article was first put up, it mentioned additional character slots:

Creating Your New Identity

Create a new modern World of Warcraft character to undertake your adventures in Pandaria, collect a variety of powerful new items and transmogs, then take your transmogs with you when you continue your adventures in World of Warcraft®:The War Within™. Additional character slots will be available so that you have room for your new fully leveled and fully geared hero to join you in your continuing adventures through the Worldsoul Saga™. All Remix characters created during the event will convert to a standard character to play within modern World of Warcraft at the end of the event.
(Thanks T)
Then it was edited to remove that portion:

Creating Your New Identity

Create a new modern World of Warcraft character to undertake your adventures in Pandaria, collect a variety of powerful new items and transmogs, then take your transmogs with you when you continue your adventures in World of Warcraft®:The War Within™. All Remix characters created during the event will convert to a standard character to play within modern World of Warcraft at the end of the event.
Any particular reason why? I know it still in development, but that was quite a big change.

Kaivax
Community Manager

#25 – April 23, 2024, 11:24 p.m.

With the Dark Heart patch, we will increase the maximum number of characters that can be created on a WoW account from 60 to 65.
Have fun!