The interesting thing about "open-source cameras" in the sense of film is, the film chemistry and film coating methods are very much trade secrets.
Making up developer from base chemicals (metol, phenidone, hydroquinone, and so on) isn't impossible and some people do it so they can "tweak" the process a little bit.
The one thing I've never heard of anyone doing is making up a photographic emulsion from scratch at hobbyist level and coating a film base with it.
I don't disagree. Commercial film stocks tend to be proprietary analogs to BLOB's. Though, for current film stocks, tooling (IDE analogs) for developing those film stocks are available (e.g. C41 and E6). Film stocks requiring proprietary development processes are gone from the market.
There are also well documented photo-chemical substrates that are relatively easy for a radically open source photographer to hack on, e.g. wet plate collodian and the more film like dry plate silver gelatin processes. Not all that practical adapt to a 35mm film camera. But analogously open source jumps through hoops to run on an iPhone.
Making up developer from base chemicals (metol, phenidone, hydroquinone, and so on) isn't impossible and some people do it so they can "tweak" the process a little bit.
The one thing I've never heard of anyone doing is making up a photographic emulsion from scratch at hobbyist level and coating a film base with it.