Groups with only one field skips the extra group wrapper around the field automatically today. This feature is causing tons of problems. For instance you can't have behavioral settings if you only have one behavior since then a parent content type wouldn't find this setting on the correct path.
Make sure the solution for this is backward compatible. Could perhaps be done by introducing a new field for group(forceWrapping for instance), a version in semantics.json or by adding a blacklist of versions that we don't support anymore and force users who upgrade their plugins to also upgrade their content types.
If we just stop removing the extra wrapping when a group only has one field content before this change wouldn't have the wrapper. After this change it would. Only one of the versions would work.
We can't force people to do run upgrade scripts without doing some ugly stuff
Backwards compatible solutions aren't possible here since the reader of the data is the content type itself not core. We would have to rewrite all content types to be backwards compatible, but again we can't force users to upgrade.