If we leave the publishing-as-a-business area, I wonder how much university libraries currently pay annually for their subscriptions. And I do wonder, if it would make sense for universities to let their libraries take care of archiving and publishing the respective uni's publications. Open-access everything, host it at home.
To reiterate, however, I think it'll still be necessary to have some sort of submission fee to cover the costs of peer-review.
A few more points: - people outside of computer sciences (and maybe physics) do not want to deal with LaTeX. As a result, they want to submit ugly word files and get a nicely formatted paper out of it (this has a cost, but not in CS where we submit nicely formatted LaTeX papers)
- most journals do not do copy-editing, but the big ones actually work on the figures, the text, fix the references, etc. Again, this is not common in CS.
Regarding the humanities/sciences division, I agree that the market is different. I think, however, that this difference is very accurately modeled by a single factor: technical literacy.
On the whole, I find that the humanities are not interested in the inner workings of computers. They do not care, and it annoys them greatly to think of such things. Now consider the fact that open access online journals are started by tech people, which is to say people from the sciences. Every open-access journal is just too damn complicated for people who don't care about social media, or even social logins. They want (query in) -> (paper out).
I think a simple experiment would be very convincing. Start a journal whose only job is to manage the peer-review process in the most transparent manner possible. University computing centers can donate storage space to the project. The now-slim editorial costs can be covered by modest submission fees -- say $100 for any non-3rd world university.
I posit that if such a system were to be developed, the humanities would latch on immediately. In other words, I suspect the humanities want more open-access and unrestrictive licensing, not less, as it's actually more convenient for them.
In short, I argue that the editorial business is resisting an inevitable market change.
Edit: to end on a more positive note, I'm sure a business opportunity exists for editors who can make present us with a convenient set of tools to work with this data.