I must say I am skeptical about how meaningful the struct update syntax is to address the readability problem. After all, if you have a long function, you likely have more than a handful of variables and you are unlikely to use the struct update syntax: we read struct fields more than we update them and best practices would suggest to encapsulate struct updates on the modules that define them, instead of scattering them around. Therefore, when dealing with long contexts, there are more general techniques one should rely on, such as using clear variable names and encapsulating logic in modules/functions.
PS: I kept this observation out of the post as it is based on my opinion (which may change).
