Filmmakers being able to bring their vision to life using generative models is going to create such a huge expansion of the market.Of what market? Certainly not film production. I have my doubts about whether it will expand the market for films, in the economic sense. The lower the cost of producing and distributing a film, the lower the monetary value people will place on it.
Look how most music artists are no longer able to survive on royalties, and a few massive streaming companies have an astounding profitable oligopoly of consumers' music interest. Yes, many pre-streaming publishers were exploitative or unethical, but I'm not convinced that it was to a greater degree than the current market leaders. Consider also that the streaming revolution steamrolled many, perhaps most, indie record labels that supported niche genres; some live on but are no longer able to sustain physical output and a reduced to being digital marketing companies.
Now, people will continue to tell stories and entertain others, so technology like this will be good for people with an artistic vision who can't easily access publishers for whatever reason. It will certainly allow people to pursue bold artistic visions that would not otherwise be economically feasible - exotic locations, spectacular special effects, technically complex perspective moves. Those are good things; I worked in the film industry for a long time and have several unproduced scripts that I'd like to apply this technology to, so I'm not rejecting it.
However, more content doesn't necessarily translate into more economic activity; I think it very likely that visual media will be further devalued as a result. People who have spent years or a lifetime developing genuine craft will be told to abandon it in favor of giving suggestions to a computer system, and those who don't will be laughed at or suspected of fakery, because fakery is so widespread these days (Relevant recent example: https://news.ycombinator.com/item?id=39379073). The easier it becomes to make something, the less value the market will assign to it; rational from the abstracted perspective of pure price theory, disastrous in real life.
Increasingly, we seem to be tilting towards a Huxley-esque dystopia of stunning and infinite-feeling virtual worlds to which we can escape on demand, and an increasingly shitty real world marked by the brutal economic logic of total resource and information exploitation. Already a stock rejoinder to complaints about the state of things is that humanity is on paper richer than ever before, to the point that bums have smartphones and anyone can afford an xbox. I have a homeless neighbor who's living in his car, spending his dying years watching YouTube on his phone to fall asleep because he's lonely. Technically this is an expansion of the market, but I don't think it's a good outcome.