I don't think so, and I think you're moving the goal posts on me! :-)
I've got a good friend that works at a large search company, and he's happy to wow me with the scale of things, particularly in contrast to when we used to work together at a different company, processing piddly terabyte files. He's currently working on something that requires every last smidge of a 64 bit integer, so I get it.
However, we were talking about array indexes, for loops, and file offsets for a single file. These are 8 byte variables within a running program.
> FWIW, the largest single data models I am aware of are not byte-addressable with a 64-bit integer
I'm not sure what you're referring to here. I don't think you're saying you have a single machine with 18 Exabytes of storage in a block device or memory map. So if that's 64 bit keys on a distributed "database", I can see that. I can also see how using 128 bit UUIDs might be wasteful at scale, so you optimize bits.
But those aren't good reasons for Rust or the C++/STL to use unsigned integers for their collections. :-)