It will be a planned migration. First announce, then discourage access to tce area, by way of website, documentation, and gui tools .e.g., appborwser.
I realize users may likely have large collections of tce currently in use, so therefore removal for support of such from core will come much later.
By announcing our plan, users can also plan accordingly. This will not happen that soon. I see several release candidates, typically a week apart, before the website changes. During release candidate testing it will only mean no obvious gui access to the tce area.