This may be impossible, I don't know that much about DLNA implementation or the JRiver MC application architecture. But from a network perspective, it should be possible...
Benefit: Separate libraries for each media type. Like in the Wiki, but on the server. This could allow for a more granular access to the media.
Hypothetical scenario:
Library server, three libraries, (1) for videos, (2) for audio, (3) for pictures. (1) is tied to port x, (2) is tied to port y, (3) is tied to port z. A client communicating via port y therefore only accesses library (2).
I see two options. Either, each client (=remote IP) is only allowed to access a single library (maybe for devices lacking proper network capabilities), or there is no restriction (for devices with full-blown network capabilities).
On the client side, each remote library is configured as server IP address plus port (i.i.i.i:port, just like it is now).
So, I could configure my HTPC to only talk to the server for the videos library, and my workstation would only have access to the audio files, while the laptop just gets the images (& home videos) library. And "some other client" could get access to all three libraries (maybe it is the ripping/tagging station). This would be cool. Like a "Library Router"...
Client HTPC: Accesses library (1) via port x
Client Workstation: Accesses library (2) via port y
Client Laptop: Accesses library (3) via port z
"Some other client": Access library (1) via port x, (2) via port y, (3) via port z
I know I could setup users for each client device, but this is just hiding stuff (the "other" media types) that shouldn't be there in the first place. I also know I could setup a VM (Library Server) for each media type, but this would be ridiculous and a waste of server resources.
PS: This is just an idea that I first had when I moved my JRiver installation to the Server (Debian VM) - Client (Windows PC) model. With the addition of more and more media types to the library, the server limitation of only one (shared) library kept "bugging" me. However, I'm aware that this might be impossible because of how DLNA implementation works, or because of the JRiver MC application architecture, or just because almost nobody would really need/use it