Here I go stepping off into the deep end.
Seems to me that a Closed System is one where the Law of Conservation of Mass and Energy is in effect.
Therefore, an Open system would not require the Conservation of Mass and Energy.
An Open system would allow for one to gain more energy from a system than was put into the system.
OK, I'll step back out of the line of fire to see who shots that down.
Coming up ...
Very interesting speculation, Slingshot. It seems you're saying that an open system is one in which the most fundamental physical law of the universe has no effect -- that would be the first law of thermodynamics. It is difficult to imagine what such a system would "look like." The first law has been interpreted as representing the basic symmetry of the Universe, and the second law, what facilitates the "symmetry breaking" necessary for things to come into existence. The second law is also that which gives us "the arrow of time": existence, unlike many physical processes, is not reversible in time....
You wrote that an open system would be one in which more energy can come out of the system than was put into it. Which just reminds me: I wonder where virtual particles "come from."
Anyhoot, your speculation or conjecture raises huge issues Slingshot! Will think about it some more.
Thanks so much for writing!