Per prior descriptions, MC 12 allows a library to be shared by multiple networked PCs, but only the first PC/user to open the library has write privileges.
My suggestion is to allow a parameter to be set (in MC, on command line, library manager setting or wherever appropriate) so that when MC is run or a library opened, that the library is only opened for read access, allowing a subsequent PC/user to open the library for write access.
Hopefully this would be relatively easy to implement and would allow a an instance of MC ("PC A") to be run a library/UPnP server with read only access (and this instance would always be on, e.g. on a server PC); then if another user/PC ("PC B") wanted to make changes to the library PC B could open the library and because no other users had write access make changes to the library. If this feature were available, I'd have MC set to run by default like PC A (which would function like Party Mode) and only when I wanted to add media, edit the library, etc. on any PC would I run it like PC B. Then I could perform editing from any PC on my network without having to shut down the server and any other instances first to give myself write access to the libary.
Given the many posts about this over the years I would think this approach would be useful for many people and with the work that has already been done to allow multiple PCs to access the same library, this additional functionality should hopefully not be tooo difficult to implement.
Of course, my knowledge of how library access is implemented in MC is conjectural so this may not be at all workable, but if it is not I'd be interested in knowing why.
P.S. If this gets put in I'll surely post about it on htt://www.peoplesrepublicof.com