Speaking a non-Cadence user (despite owning a copy), I tried using Ultralibrarian and similar and realised they are a waste of time. There were various reasons, but the primary one was consistency. Things like layer references would need changing and that's if the same layers were used for the same thing across models and sources. Then there is the preferred house style, and just as you wouldn't want your parts numbering scheme tied to match that used by, for instance, RS I don't think a house style should be dictated to by a third party library source.
Some of those things aren't a surprise and the providers try to cover all bases, but in the end I realised the main reason I went looking for library parts was because I didn't have the creative vision to imagine them. That is, I'm not an artist and how should some reasonably complex part look? Finding someone elses idea is generally why we seek them out. Once over that hurdle, which involves making up your own house rules (all inputs on the left, etc) you can generally draw the schematic symbol in the time it takes to go and find one. The PCB package I would want to verify is correct too, which means figuring it out from the datasheet, and it's just quicker to do that from scratch than it is to get one and then try to measure it.
Now, the only thing I go looking for is 3D models, 'cos those are pretty tricky. A reasonable excuse for doing that is to verify that the PCB package is correct - sure, the 3D model might be wrong, but a false negative is cheaper than a false positive (or just trusting to fortune).
The idea of a took such as yours might be attractive to new users, I think, but once they're enmeshed in the ECAD product and doing professional work it's probably not going to save much effort. To be of real benefit it would need to take those files from diverse sources and change them to be like the (definable) house style as well as importing them.