I like theories like this, they are good for paradigm shifts.
A part of the initiates discovery of the 'speres' in my culture describes a few of these realms and access to them from both unconscious volition and a determined physical approach.
Whilst Ive experienced both unconscious and 'light bulb' revelations Ive yet to see an actual determined physical approach.
Its more than likely that a multiverse view is the correct one for me as a monoverse just isnt a sustainable idea really, considering the duality of our universe.
I think past life experiences could fall into this catagory too as my cultural belief describes so called past life as co-existing realities, hence the easy access to some memories, feelings and coincidences.
Certainly wave dynamics indicate multiverses by the mere process of just being a wave, go up out of range then go down out of range and all we see is the in-betweens.
And yet, its more than possible that none exist at all and that were are just memories of an instance in time that because of the vastness of space, perpetuates as echoes maybe...?