It's more hand-wavy than it's admitted. When you think about it, the idea of emergent phenomena amounts to:

- There's no underlying consciousness or conscious originator (no god, no panpsychism, no underlying conscious layer at the basis of reality, no nothing) - At some point, two or more elements (rocks, atoms, etc, that weren't conscious), aligned precisely in a given configuration and zap!, they became conscious and interactive - All consciousness then sprang from that.

So the question would be, if systems favour inertia, stasis and conservation of energy, why would there be consciousness at all and just not an endless void, or a perfectly stable (as in homeostasis) system without conscious agents, or just rocks floating in the space.

I'm not saying the idea of emergent phenomena is wrong, just that you better answer the complex questions other "supernatural" theories try to address, before declaring it some sort of obvious and correct answer.

It is as good as any sensible hypothesis: it allows us to focus on a more promising direction of research.

A hypothesis is an unproved proposition that is actually susceptible to proof (or disproof). That is, it must make testable predictions.

What predictions, testable in principle, are made by this "emergent phenomenon" hypothesis?

Well, philosophy is different from (positive) science in that regard. Yes, you have to realize that the notion of emergent phenomena belongs to philosophy, where a hypothesis (it can be said that philosophy consists of hypotheses) can only be "proven" indirectly, from relevant experience (such as scientific research).