This list is dedicated to exploring the implications of the prospect that all universes exist. According to this principle, universes exist with all possible laws of physics.
So by "all universes exists" you mean "all physical universes" exists?
It follows that universes exist which follow the MWI; and universes exist where only one branch is real and where the other branches are eliminated.
In that case you get universe + multiverse + multimultiverse + ... ... + ... big renormalisation problem. But that's ok. I mean it is the same with comp and the view from inside "numberland".
Universes exist where the transactional interpretation is true, and where Penrose's "objective reduction" happens. I'm tempted to even say that universes exist where the Copenhagen interpretation is true, but that seems to be more a refusal to ask questions than a genuine interpretation.
OK, but only as harryPotter sort of "universe". Actually I think "universe" is a very fuzzy term. Laws of physics emerges on the many consistent histories/computations and are always essentially probabilistic.
Therefore it is somewhat pointless to argue about whether we are in one or another of these universes. In fact, I would claim that we are in all of these, at least all that are not logically inconsistent or incompatible with the data.
That is, our conscious experience spans multiple universes; we are instantiated equally and equivalently in universes which have different laws of physics, but where the differences are so subtle that they have no effect on our observations.
So the need to make a quotient by the indiscernability equivalence relation.
It may be that at some future time, we can perform an experiment which will provide evidence to eliminate or confirm some of these possible QM interpretations. At that time, our consciousness will differentiate, and we will go on in each of the separate universes, with separate consciousness.
It is still useful to discuss whether the various interpretations work at all, and whether they are in fact compatible with our experimental results. But to go beyond that and to try to determine which one is "true" is, according to the multiverse philosophy, an empty exercise. All are true; all are instantiated in the multiverse, and we live in all of them.
So I agree modulo the ambiguity in the word "universes" especially with relation like "we belong to ..."