Maintaining two systems would indeed appear to be more work, and I can understand the concern of it raising the workload of the librarians. But I also think of a pending repo system to be more of an extension of the current system that allows faster community assistance.
I envision an ideal system would consist of some of the following points:
All editing of the part and submission of changes would happen within a Kicad plugin. The use of wizards could probably help generate KLC type libraries with reduced mistakes.
Technical challenge: wizard development, plugin system, schematic/footprint/3D editing systems.
It would have all automated checks to submit parts to the pending library(ie with a 90% pass of a weighted test) that is a repo on git. I'm not completely aware of the automated testing systems used by the librarians at present. The pending library or plugin would not come with a standard install and would need to be added after. It would still require a valid github login.
Technical challenge: Automated submission through a git client accessible within Kicad. Must track and allow edits/comments from github.
From there users could edit parts based on the comments of the part and the reasons it had been previously rejected. If the user has made the required changes the part could then be submitted/flagged for librarian review. If rejected, it stays in pending with the comments or reasons for rejection until the next time one of the community chooses to use/modify the part.
In open source terms, I believe a system like this would allow parts to more easily churned through the bazaar before being sent to the cathedral.
Ideally this would mean that the librarians unless making a part from scratch themselves would only be looking at the parts that have been submitted by the community through the as yet to be developed plugin (Kicad Integrated Pending Public Engagement Repository or KIPPER for short )
This is of course theoretical, and without the requisite technical solutions to the above challenges hard to move forward on.