A Mukti very close may not be fully enlightened in the sense of I am Brahma but definitely they are enlightened. The Upanishad is trying to teach you realize yourself as Brahman here and now. This is what this silence beyond now we shall try to explain that yes the other smaller heavens H which will come into existence at a point of death.
Swami Sarvapriyananda teaches one of the shortest and most profound upanishads accompanied by Gaudapada's Karika. This lecture covers Karika 22-23 and Mantra 12.