"summary": "Sally read a blog post",
Is the example in activity streams, which is a completely different use case.
The Read Class use case, as covered above is something in an activity stream. For example you click on facebook and it says "Dan just liked your Post" -- thats an activity. Its a time oriented list of actions.
The time invariant version of this would be Post is liked by soic : num_views people, liked_by : Dan, Elf, Alice
I'm noticing the same issue in schema.org -- i tried to find a bookmark item. Easy, you'd think right? But no, it only has a BookmarkAction -- which is like a BookmarkActivty.
I think it's worth delineating these two use cases.
As such, would it be possible to get viewed_by back on the radar, or would you recommend finding a home for it elsewhere?