For Andre's question, the short story is that you should test it and see :)
The longer story is that these limitations are due to swift keeping these listings. Once the number of objects in a container gets in the order of magnitude of millions, the containers can only handle on the order of 5-10 updates per second (on regular SATA hardware, and on the same nodes as the object servers). This of course is going to vary based on your actual hardware and use cases. If you don't need to write to a single container more than 5-10 objects per second (or if you do, only in bursts), then you should be fine for many millions of objects (though I doubt for a billion). This is just something that you would really have to test for your use case. You will know when the container servers are being overloaded by watching for async pendings on the object servers to stack up.
Similar limits apply to the containers. The more containers you have in an account, the longer it takes to create a new one. I haven't really tested this, but my guess is that with a similar setup as above, for a given account, you would only be able to create 5-10 containers per second, and like everything else, this should be tested :)
All of that said, even if you adopted a lower end limit of 1 million objects per container and 1 million containers per server, that is a lot of objects :) (1,000,000,000,000).
If this is a private cluster then you could also leverage accounts, and there are not really any limitations around accounts that I can think of right this moment.
There is one other option that I have thought about before for use cases like yours, and this would require a bit more work. It is conceivable that you could add an option to swift to ignore listings, and would bypass the parts that need to do account/container lookups. Since you are tracking the metadata outside of swift, not having container/account listings should be fine, and this would free up all of those limitations. This is not a feature that is on our current road map, but if it is something you are interested in implementing, let me know and I can help you get started on the right path.