Humanity arrived at a locomotive at the beginning of the XIX century, while the first viable industrially produced colour film was produced only in 1935 (KC itself).
To me this means that "a locomotive", a generic one, is intrinsically less complex than a Kodachrome, as the former is a "XIX century technology" product. I am sure later locomotives are much more sophisticated and require XX century technology. But that again is not the point.
Designing a modern locomotive and designing a film are certainly both extremely complex tasks. Designing a "typical XX century locomotive" is XX century technology just as it is KC. If it wasn't equally complex, humanity would have arrived there earlier. So a locomotive incorporating technology that was new in 1935 is certainly not easier to build than KC, in principle.
The problem here is that you can make a single locomotive, or a single luxury car, and replicated it artisanally, and it might have a market, and a manufacturing sense.
You can build 1 car / year in your garage, it may cost $300.000, and you can find buyers for it, and be booked for years. Or you can think later about industrializing production. I think the same can be said for locomotives. You can - as historically happened - start building a few, and only later industrialize the process.
The problem with KC film is that it is not something that can be produced in a garage and be economically viable. It is, so to speak, a product that is "intrinsically industrial". Other, simpler kind of films have been produced "in the garage" first, and only later industrialized.
The problem with KC is that its complexity (of the entire process up to the slide, not just the film coating) cuts out any attempt of garage production which is economically viable. You can't make a "luxury film" that costs 50x a normal film.
Expert and determined, and rich people, can certainly coat KC in the garage, and develop it in the garage. But at which costs? $300 per roll?
So the idea proposed is that garage production is just a first step, a way to demonstrate to a producer that the product is feasible.
With KC I see no hypothetical need to develop a demonstrative garage production, and then use it to propose it to an industrial manufacturer. No need for demonstrations. Any industrial film producer must be able to produce KC, it is old technology, it is described, the patent is available, so anybody in the industry can certainly produce it.
What is lacking is not the access to the technology, or the industrial capability.
What is lacking is the perception, by a producer, that there is a potential market, for this product, in such a volume that justifies its production. And unlike a B&W film, small volumes would not work.
Fabrizio
PS TIP is in my view a misleading comparison, because people at TIP could not use some chemicals of the original formula (which is not produced anymore due to environmental reasons, IIRC). So TIP has had to work around difficulties, to "reinvent" the product, it is really a new product and it shows in the results (what I have seen so far is just awful, a colour film works when the sky is blue and the grass is green).