Dear Marc,
Indeed I might also describe my view as a monism, more precisely a mental one, since, as I wrote, consciousness can understand mathematics, but mathematics cannot describe consciousness. However, mathematics is then a remarkably stable part of this mental realm. And we (I mean, some people) have straightforward abilities to describe mathematical systems, that cannot be applied with such a success to non-mathematical ones.
"I am fully aware of this, but what can I do? Suppose it is true that capital-E Existence ("All that exists") does indeed follow from the most simple rule imaginable, "Everything Exists","
What can be done: notice that science is no more in its infancy, and that we do already have some effective materials to consider. Namely : is existence described by a probability law or not ? We did find one important probability law, that is the Born rule. So we know that a probability law exists, and we can already describe it. Then, in case we feel lost in our speculations on the nature of existence, we should not forget that there is this thing we know, that needs to be taken into account, so that our ideas remain compatible with it. Now what I criticize about Moravec's explanation, is its incoherent way of presenting arguments that are actually based on probabilistic assumptions (outside which no such arguments can make sense), while trying to deny having any clue on probabilities. My suggestion is to work on clarifying the structure of the probabilistic assumptions that these arguments are implicitly based on. Then, are such probabilistic assumptions compatible with the Born rule ? If you admit a non-probabilistic distribution of existence (i.e. not described by a measure), then in such a framework, how can any probabilistic law such as the Born rule make sense at all ?
About the flow of time, I wrote that we have an available analogy with the time of the foundations of mathematics, which I described in my site. So time has a sort of structure for which we have a mathematical analogy (better than the pure geometric view of linear order), yet it is only an analogy which does not suffice to describe the effective contents of consciousness and its time flow.
"qualia and the flow of time are not structures. What are they then?"
What sort of answer do you expect ? If a mathematical description was given, it would make these things mathematical. However it does not mean that it is a complete mystery, since, anyway they are things we somehow know by personal experience (unlike the concept of "nature" put forwards by materialists).