I don’t see how shared dreaming could be possible within the materialist world view which I happen to disagree with. Part of this paper by Peter B. Lloyd here covers why telepathy is unlikely under the physicalist view:
easyweb.easynet.co.uk/~ursa/philos/light.htm
“Transpersonal communication is, I think, more than just telepathy. I believe it plays a crucial role in healing. First, though, let us consider the basic problem. On the physicalist view, individual people are separate physical systems, isolated by distances in space. If any information is to be communicated between two people, it must be expressed in some physical format, such as sound waves, or ink marks, or visible movements, and transmitted through the intervening space to the other person, who must then interpret the contents of the physical medium. For instance, when you hear someone talk, vibrations in the air travel from her lips to your ears, and your brain interprets them as syllables of English. From this perspective, it is impossible to countenance the direct transmission of thoughts or feelings from one mind to another. There have been speculations for many years that telepathy involves broadcasting signals in some band of electromagnetic energy, or in some undiscovered form of physical energy. The weight of evidence makes this implausible. First, it is a basic characteristic of the emission of any physical energy that its strength diminishes with distance (in accordance with the inverse-square law); yet all the reports of telepathy that I have seen suggest that its efficacy is wholly unaffacted by the distance between the participants. Second, if people can receive these transmissions, then there must be an interaction between the telepathic energy and tangible matter (unlike, say, neutrinos, which can pass through whole planets), therefore the strength of the broadcast must be attenuated by intervening obstacles, and if the telepathic energy were electromagnetic then a metal box (a ‘Faraday cage’) would block it; but telepathy seems unimpeded by any obstacles. Third,if everyone’s telepathic broadcasts are released into the atmosphere, how can anyone pick out a particular sender’s transmissions? Compare this with conventional radio communication, where the broadcaster must decide to transmit at a particular frequency, and the receiver must tune in to that same frequency. This is not proof, but personally I find the notion of a physical basis for telepathy implausible.
If we adopt the Berkeleian philosophy, though, we get a different picture. Here, we deny that space actually exists: it is only a construct within our imaginations. Therefore our minds cannot be at any distance at all from one another. Hence the whole problem of sending thoughts and feelings across long distances, which bedevils physics, does not arise in the Berkeleian system. Furthermore, no mechanism is required to express thoughts and feelings into a physical form. For, each individual’s mind exists within the matrix of God’s mind: we are, in effect, parts of a single, vast mind and we may therefore suppose that transpersonal communication is achieved through the same means as intrapersonal communication. Just as you can have awareness of the thoughts, emotions, and memories in your own mind, so telepahy involves the access by the same means between two minds.”