Currently, we need to invent in-house bicycle solutions to keep both the extension library source code and the up-to-date customization XML files under the same source control folder.
The workflows for the extension library and XML-based customizations feel very segregated, however often you need both as part of the same project. For example, to customize business logic, I strongly prefer to work in Visual Studio, whereas for the interface, you have no other option but to use the Customization Manager interface.
It would be really convenient to have a unified out-of-the-box workflow to maintain both the XML and the extension library under the same source control folder.
Basically I would propose to widen the extension library solution format to also include the _project folder by default, accompanied by a tool that:
Can download the changes to XML from the specified Acu instance (so you can commit those to git)
In case changes are made locally to the XML, publish the customization back to the specified Acu instance
Build & package the whole thing as a self-contained customization package to be imported on other Acu instances.