This is an odd request, but it might be extremely useful for people who do multiple stories within one setting: I would like the ability to include an external scrivener project as research material within a scrivener project.
The idea would be that the binder would show that scrivener project’s binder within a folder of the root project. The files within that sub-project could be edited and the changes would be saved to its own project rather than the open project.
Why? Because world bibles are extremely useful and not trivial to copy from project to project unless it is compiled first, which makes it harder to edit. It would allow two or more projects to have a shared “bible” that can be edited from either and never fall out of sync.
Complications: Recursive structures, which could be solved by making ignoring self-references; memory usage, since the binder could become quite large if multiple projects are being sub-used. I am sure those complications could be overcome. Compiling, since the sub-project would have a compilable part which would have to be ignored somehow. I assume this reference wouldn’t be placeable within the manuscript, just as PDFs can’t be.
Having multiple different project binders in the same sidebar sounds like a total programming nightmare to me, given how the binder is designed. I wouldn’t place any hope on that specifically becoming a possibility.
But the technical issues aside, would also be a lot of extra complexity to provide a level of integration that is only marginally better than what can be achieved with the latest designs. To wit, Scrivener for Windows will be adding new features (some of these may even already be available in the beta version) to better integrate two projects together. I posted some of my techniques previously. Even if you cannot adopt those techniques immediately, hopefully you find them useful in the future.
Out of interest, why can’t you just use one project rather than several? Have your world bible in the Research section or wherever, and then each book in the “Draft” area (which you could rename “Drafts” or “Manuscripts” or “Books” or whatever). Although it’s traditional to have one project per book, you can have more than one book in a single project if that makes it easier to organise.
Because I use both Windows and iOS versions and large projects can sometimes have dramatically large sync/load times since mobile and desktop use different files. (hypothesis)
Sub-projects wouldn’t fix this. You’d still need to transfer the entire contents of the sub-project to the device in order to use it, and it would still use the same underlying file format.