Maybe he is Dimitri. That would explain some of the things he says.

The article is gone now. I wonder what he means by "physically possible" when he says that every physically possible universe really exists. If "physically possible" means "not contradicting the actual laws of nature", shouldn't there be, say, a universe with only empty spacetime? But aren't the other worlds supposed to branch off from a common origin, which would rule out such universes?

Oh, I am sorry for quoting so many non-free articles these days...
From what he said I just imagined him having a kind of Lewisean possible worlds theory, except that for him "possible" means physically possible not logically possible. Which means "not contradicting the laws of nature". Anyway from what he said it was certainly not possible to understand a multislit experiment, since it didn't explain why at all the universes where the photon is taking any possible path would interfere. But maybe I didn't get the point because I don't know enough philosophy. What I found compelling is that he intends very much to take QM seriousely and is very fiercely opposed to any such as claiming that physics doesn't describe the way the world is.
But on the other hand, QM doesn't provide a proof of existence of any other universe than ours. There is very much space for speculations about what it really means from a metaphysical point of view.
And does physics really exclude a universe where the electron mass is different from 511 keV? As far as I understood this, it makes perfectly sense to talk about theories containing particles with very different masses, or no masses at all. We do this all the time. Particle masses are free parameters in the Standard model. And there is no other theory, with any experimental support so far.
But of course I might be wrong, since I really don't want to claim that I understand much of this business