Well, I used to be part of a darkroom where people would create their own films and plates, and you learn that manufacturing physical objects is relatively easy now, but manufacturing film chemistry at a consistent level is bloody difficult. Physical build monitoring is straightforward, but feedback cycles with chemical and pollution monitoring isn't. The level of consistency is mind-blowing for motion picture and still film. Any idiot can make bulk craft beer (and indeed does) but few idiots can make a delicate lager with little headroom for error.

People have been using wet plate photography for years. Others have started using dry plates, and someone is selling them commercially.

Then there is a community working on the above and a few working on true roll film.

Probably the best site for making your own materials is http://thelightfarm.com, good discussions about all films commercial or homemade at http://apug.org

Film chemistry is very complex and no small scale production has been able to match the quality or quality control of Fuji, Kodak or Ilford.

To expand on this: the problem isn’t putting out one batch of high quality film; it’s putting out batch after batch that performs exactly the same. Nobody wants to lose an important shot because this batch of film exposes a little differently from that batch or has slightly different color response.

Any craft brewery can make an outstanding batch of beer, and many do it quite often. The miracle of Budweiser is making zillions of barrels of Bud and Bud Lite that are indistinguishable from one another year after year.

It's not really like that. Either you can coat a 5000-foot roll of acetate with 14 layers of chemistry to a high degree of uniformity, then slit and sprocket the film, and package it, or you can't.

Black and white or color?

There are at the moment only 2 large companies (Fuji and Kodak) what can produce color film and one company (resurrected Ferrania) what will in the long term maybe trying to do it. There is one company (Ilford) that maybe potentially could do it when they wanted it but so far they do not.

Any other color film you see on the market is either rebrand of some old or new stock.

There are a bit more B&W film producers:

Fuji (again) Kodak Ilford Foma Adox Agfa Photo (I could not recall which of the old plants in EU is producing actually the product) Bergger Silberra Ferrania

There are perhaps some few more that are producing B&W film.

The last 3 are pretty much your definition of boutique market for film. It exists but it is not grande. Even Fuji and Kodak marked is not large but it is growing.

Kodak has their own dedicated waste treatment plant. You would face similar obstacles.

In theory there would be, but it depends on how much people are willing to pay for it, how long they're willing to wait for it, and whether you're flexible enough to not be producing until an order comes in.

I'm sure similar questions are asked about things like floppy disks / readers, or old 486 compatible CPU's which are still in use here and there, or CRT displays.

Probably extremely hard and cost prohibitive you’ve essentially lost all of the economy of scale that used to support this and more importantly the first hand knowledge and expertise in building those machines in the first place.