Science

I see two likely possibilities:

• Qualia is a property that emerges spontaneously in systems that process information. There might be a threshold of complexity at which it emerges, or it is always there and it scales in intensity with the complexity. Living things did not evolve qualia because it is useful, our qualia arises spontaneously because of the complexity of our brain.
• Qualia is a property that requires a very specific set of circumstances to emerge, and living things actively evolved to have qualia because qualia serves a useful purpose.

I agree with what you say. I would call the process of working on the internal model "thinking". It would in principle be possible to have a system that thinks just like we do and appears to possess qualia, but it does not. Unless the scenario (1) is correct - and qualia will spontaneously emerge in a complex thinking system - which I think is the case. So, qualia is a necessary byproduct of our useful internal model processing.

As you have said, we can make the reasonable assumption that systems that behave as if they have qualia have qualia, then we may proceed doing useful things in this field. We may design new types of useful conscious systems, have discussions about AI and animal welfare ethics, etc.

As to:

It’s of course impossible to say definitively whether a system has qualia of experience or not

II interpret this as if the answer of the hard problem is "we can't solve it, because it is fundamentally impossible to measure qualia". Measuring qualia is essential to address the hard problem, because if we can't show that a system has qualia, then we can't show the conditions under which it arises.

I imagine that the work on AIs is the most likely path towards figuring out the hard problem. We can test such theories by constructing neural networks that produce the desired behaviors and then seeing whether the observed behaviors match the predictions.

I also used to think that AI was the best way. Recently though, the paper of training neurons to play ping-pong blew my mind, because they practically showed that you can apply negative and positive stimulation to a simple network of neurons by providing it with either predictable or random information. I am not so hopeful about the hard problem being solvable, but seeing work like this gives me hope.

I think that qualia is one of the most (if not the most) interesting pieces of nature. To me it is practically super-natural. The laws of physics as we know them can describe our world without a hint of qualia, and the unieverse just randomly decided to sprinkle the gift of conscious awareness on us for no apparent reason. It is so ubiquitous (i think) and yet we can't answer the simplest questions about it with certainty.