Blizzard have clarified one of the common community questions these last few days, as the Shadowlands Timewalking/Chromie Time campaign will indeed be coming with phase 2 of the pre-patch, and not with Dragonflight launch, as initially feared. This means the level cap on all Timewalking campaigns will increase to 60 on November 15th/16th and you will be able to level to max using any of the existing campaigns, and you’ll be able to play the Shadowlands campaign from the start with a new character (for veteran players). 

Chromie Time (Source)

Thanks for asking about this. We’ve just updated the article with the following:

If you’d like to select a different Timewalking Campaign, simply speak to Chromie again. Beginning with phase 2 of the Dragonflight pre-patch, Timewalking Campaigns will scale to level 60. The Shadowlands campaign will be available as a new option for veteran players once Dragonflight launches.