It’s a natural idea and not a bad one, but understanding the issue requires knowing the 1000 former discussions about this. I wish this would work, but even without having been tried such a collaborative repository myself I understand too well that almost any attempt without a centralized management and dedicated personnel will fall apart quickly.
To add something constructive I throw out an idea about footprints. If I find a ready made footprint somewhere I usually need or want to modify it somehow. Not necessarily to make it correct for a working board, but because it’s better to make it follow my “standards” and needs. If we had a repository, it should still need to have some kind of quality control and standards, and that makes things difficult. As with the official library, people who basically want to share their footprints pretty quickly notice that to comply with the requirements (KLC) they need to virtually remake the footprint.
This would be much easier if the footprints would be minimal. The critical part is the pads. They are described as “suggestions” in the datasheets. Apart from that, the only objective information which can be found out without interpretation and variance between human beings is the component outline which in KiCad is drawn in the Fab layer. I suggest that if there would be a repository with any rules, the rules should be simple: the footprint has only the pads (and holes) as suggested by the datasheet, and the simple component outline without extra markings in the Fab layer, and nothing else. That way anyone who uses the repository know that the footprint must be modified but gives objective information about the component and nothing “customized”.
A similar idea about symbols would be to have only pins with numbers and names, and nothing else. The users wouldn’t need to type that information themselves but would need to customize everything else, including units, graphic shape and pin orientations. This is of course reasonable only for complex components like ICs.