The teapot technique is how Mark Osterman at the George Eastman House still teaches it - or at least did up to a few years ago; not sure what the situation is now. But it's a tried-and-tested technique. I think Jason Lane does something similar with his glass plates. One of the challenges apparently is to minimize the drop that tends to flow towards the back of the glass plate and indeed 'artisanal' glass plates (old & contemporary) can apparently be identified by this feature, which generally manifests as a trail of emulsion running diagonally across the back of the plate from one of the corners.
Other technical challenges are things like preventing frilling along the edges etc.
In any case, the technique works, but AFAIK it's mostly done with glass plates. I'm not sure if it can be made to work with film that could be loaded into a camera. I do imagine that sticking a piece of polyester film (or similar) to a flat surface (e.g. glass) might work in a similar way: stick polyester to glas, pour emulsion on, let set, peel polyester off of glass, let dry. It will curl quite badly, probably, which then will have to be dealt with by e.g. coating a second emulsion on the backside (to create a 'counter-curl') or perhaps the problem can be minimized by adding a plasticizer to the photosensitive gelatin emulsion. Likely it's going to bring a whole new set of challenges, but I'm sure someone has already tried it, somewhere, sometime. I wouldn't hold much hope making film suitable for 35mm or 120 format cameras; sheet film in e.g. 4x5" or 5x7" sounds like a more feasible endeavor. For roll film formats, I think some kind of hopper (like Ron Mowrey / Photo Engineer had made) is really the most feasible way to go.
"If they were doing it in a lab 50 years ago, you can do it in your kitchen today."- unknown
Never underestimate what people were capable of pulling off in a lab in the 1950s. Seriously - the 1950s weren't exactly the dark ages in terms of technology. As such, I really have to disagree with this statement. In the 1950s, several firms were making color film in a lab setting for testing, and of course also at an industrial scale. I haven't heard of anyone making a working color film at home, although it was perfectly feasible in a 1950s lab!