TYPO3 Core

as long as there is no plan how a site package needs to look like this can't be promoted.

IMO something like b13/bolt must be shipped with the core and then this is at least a starting point.

as long as there is no plan how a site package needs to look like this can't be promoted.
IMO something like b13/bolt must be shipped with the core and then this is at least a starting point.

There is a sitepackage tutorial. This is also mentioned on the TypoScript docs page Add TypoScript in the backend, so if you go to the documentation, that what is in the sitepackage tutorial propagated as best practice:

It is best practice to use a Sitepackage extension to bundle various configuration in an extension. See TYPO3 Sitepackage Tutorial.

And a companion extension https://github.com/TYPO3-Documentation/TYPO3CMS-Tutorial-SitePackage-Code

I was not aware of b13/bolt

Anyhow, this can be done in several steps, e.g.
1. make information about cache flushing available
2. make decision which course to take (several possibilities between 2 extremes, one extreme would be dropping EXT:tstemplate entirely, the other are promoting one or the other).
3. etc.