As I read up on the various database types (as opposed to, well, doing any actual work... [It's research! It is!] :-\ ) one thought occurs: if Apple opened* up its Managed Object class to different backends, which is currently it's limited to XML, SQLite and I think one other format that I can't quite remember and don't think is important enough to go look up, they would have a killer data storage system! :-)
Mix that with something like ZFS for the file system and you have a system, for the Mac at least, where the (local) network, pretty much the entire internet, and the machine become indistinguishable as distinct entities! That would be cool.
Now, if they could only get past their "this is an application" hangups, they'd usher in a new era of computing instead of gilding a lily that desperately needed gilding, but wasn't actually advancing much of anything.
*Apple doesn't allow you to see how its foundational framework works; you get the headers and that's it. Changing it on the fly, using Categories (aka "mixins" or (sort of) "extensions") might be possible, but it would be in breach of their license and you'd have to be on top of it all the time. In other words: not worth it; we need Apple to figure out the potential of their own technology.