Today at the root of your operating system is the file system. It would be interesting if the file system was changed to essentially the concept of a simple object store. In much the same way we have "standard file formats" today, we could move to something like a "standard class". Objects would be a first class citizen in the OS. I think this becomes more interesting too if you start to ignore where the object lives. It doesn't matter if an object you care about is local, or on a server in your enterprises network, or if it's a thousand miles away.
The second big change, is I would do away with "applications". opting instead for a smaller unit of executable. Probably integrated with the object system. The idea here is you don't buy an entire system from a single vendor. You buy features from multiple vendors... and the design of the OS makes it really easy to integrate together. I guess this is kind of the unix philosophy... but maybe taken to the next level.
Thirdly, I think it would make sense if the system was natively "reactive", I think that would help with making aspect-oriented programming more normalized.