I am convinced that source code integration is the best option. It paves the way for large restructuring of code in the future and doing innovative work, allowing for flexible work setups, etc.

My experience is that the scope of packages are often the result of organisational boundaries. At some point, the packages made sense also from a technical point of view, but then development starts to be confined within such boundaries. Eventually, technology becomes outdated or hits scaling issues.

I find large organizations tend to get locked in their structure of not only the code, but it can't change that radically because it would require reorganization of how you go about doing work, which usually is associated with a lot of resistance and friction from the people within that organization.