Regardless of the state of the content repository by the time Tasha's Cauldron of Everything will be released, I will be creating the content such as the archetypes, spells, items, tattoo's and feats for it and I will share them here.
Also, even though the current version of Aurora is closed for updates, I have been looking at making it possible for the variant features that will be in the source book. I have an experimental version of Aurora that has working variant features (limited testing done) that I plan to make available for supporters to bridge the gap should starting a new version be possible.
Existing content does not need to be modified for these variant features to work. All you need to do is create the feature and add 1 additional line of XML.
Note: some features in the source book will simply still not be possible.