I agree, I do have multiple issues with this FEP (I’d say it’s insufficient clear in many respects, and the thing about inlining an abbreviated form of the collection object can be at odds with JSON-LD), but they do not matter very much in practice. I missed the fact that target was not a valid property for non-activity objects (and would clash with the meaning of target in activities). This is not a practical issue for this specific use case either, but that’s not great.
Nevertheless, I think the initial Mastodon implementation will be based on this, considering it is almost done, and the NLNet fund deadline is mere days away…