So a modern system OS must have:
-Memory protection.
-SMP support.
That much we all agree on. Hence no flavor of AOS can be considered modern(?)
It must run on new and any available hardware, but that would exclude pretty much any OS.
It must be able to run Skype, Office suite and the newest games, personally I don't consider those to be a part of an OS.
It must used 1000 times the resources of an old OS to do the same basic things.
So no real consensus can be reached, other than MP and SMP.