So, when it comes to dependency, I see creating modification package is the only way to go about it and that too with limitation that the optional package should not have an entry point of its own. I believe there is always that option of capturing the main and dependent package as one single MSIX package (not very viable though)
Anyways, do we have any functionality in place for MSIX package such that they can interact with a locally installed app. For Example the main package is locally installed and the dependent package is MSIX. On launching locally installed main package, the MSIX package is loaded in its context, something like RunVirtual in App-V?