I wouldn't be surprised, but I don't know.
Somehow religionists believe that God can exist external to space-time but be active in space-time. Intellectually, how is that different?
I have no scientific knowledge of these theories, so I can't comment on their scientific value. My point is a simple, logical one.
1) We only have knowledge of things which we apprehend.
2) That which we apprehend exists in our universe.
3) Assuming that other "universes" existed, we could not have knowledge of them because, if we did, they would have to be connected to our universe (2), hence, in actuality, they would have to be another aspect of our universe.
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Your question about God's transcendence versus His immanence is a very profound one. Perhaps the following will help.
First, consider what God is. God is Being itself. Being or existence is what God is. Being is God's essence. Everything else that exists participates in God inasmuch as it exists; being or existence is not of the essence of any other thing. (For example, existence does not belong to my human nature, since my human nature is perishable.)
In God, Being and Essence are one.
Therefore, every other thing that exists is in God, inasmuch as it has existence. This explains God's immanence. God is in all things inasmuch as all things participate or share in His being or existence.
Yet God is simultaneously transcendent or "above" all things, since He is the "source" of His own existence, i.e., he depends on nothing else for His existence. He is Existence Itself.
So God is infinitely superior to every other thing that exists (His transcendence), while He exists in all things (His immanence).
Then God is the multiverse.