I am in this discussion on Dave's side. The only interesting use-case use-case i see currently is that changing the storage type could provide an easy means for a developer to revise in a release an earlier decision about the storage type. This ability could save the developer from the need to write a change script. I don't see the need e.g. for an end-user to say "please store this revision as file or text".
From the data-model i would also conclude that the original intention of the design was not to change the type during revisions, so the current *interface* has a bug. It seems quite natural for me to save uploaded files with the storage type file and input strings of a form as strings (the lob type is a candidate for deletion in my opinion). Providing an interface where one adds once a file and once a string is unusual. If one needs such a feature, it could be easily provided with a custom type, using storage type "file" and a custom attribute "content" of type text.
So, why not keep things simple and remove essentially the storage type option from content::revision::new, and mark content::revision::update_content as private for the time being. This change is essentially a bug fix.
If there is indeed in the future a strong reason for making the cr even more powerful by allowing to switching between storage types, this should be tipped again.
-gustaf neumann
