Denny said:

I think the assumption everything has exactly one type is oversimplifying

The assumption that everything is of multiple types is over-complicating.

Usually you can tell from the first sentence in the Wikipedia page.

"Tuesday is a day of the week"

"Love is an emotion"

"(Roman) Catholicism is a faith"

"Gollum is a fictional character"

"HAL-9000 is a character"

"Noah is a Patriarch"

"Enos was the first chimpanzee"

So consensus certainly is being achieved among thousands of authors about the fundamental type of thing each of these pages represent. Disambiguation pages very commonly reference these types of things as in "Enos (chimpanzee)".

Let's take Gollum. I can imagine a topic map has these subjects:

1. Character

1A. Fictional character

1A1. Fictional person

1A2. Fictional animal

1A3. Fictional ghost

1A4. Fictional god

Another equally valid assertion is that Gollum is a Character that is typed as Fictional and Human thing (both these adjectives that are instances of owl:Class) -- so that a comprehensive system sometime in the future would reinterpret that Gollum is actually a Fictional person.

As you say yourself, it's not useful to create a "perfect" system to handle every imaginable edge case **to the extent that they exist**. Personally I don't believe such edge cases can be found - I challenge anyone to provide me such an example.

But more to the point of Wikidata. I don't believe for a second that WP will be reorganized into thousands of namespaces. Rather, I believe first, SUBOBJECT names must include the idea of 'namespace' for the efficiencies gained, and second, WP pages should be associated with the same set of nouns (noun-phrases) available for subobject names. IOW, it's an implementation issue whether a wiki's pages are named using these namespaces, so that the wiki as a whole can gain the same inherent efficiencies I've sketched for subobjects.

Best - john