Hello cyberdyno.
This may be releavant.
Fresnel and, seperately Stokes both tried to explain the negative result of the MM experiment by some sort of ether condensation or ether drag effect. Both were proved to be unworkable explanations.
Reference: Historical introduction to a translation of The Principle of Relativity: an Original Paper by A Einstein and H Minkowski. These facts probably appear in many other histories of the subject.
With regard to the presence of empty space independently of the uiverse i believe the accepted view is that before the universe "began" there was not even empty space.
If the ether is unobservable i would take this to mean it is undetectable. So it must have no measureable properties. So there is no nature of the ether to be understood or misunderstood.
If you, however, do understand this undetectable ether, please excuse my ignorance of the subject and give me your explanation of it. No references please, just your interpretation.
Matheinste.