However, when winenous wrote "formal", this referred to my post #4, which again referred to the original example in post #1.
I discovered that afterwards...
Don't you think that "dette" can be replaced with "disse" (or "desse" in the nynorsk example), and that "disse" would seem a bit more formal?
I don't see why that would be more formal. I have never come across the topic in any prescriptive book on how to write Norwegian and it does not seem to have a basis in cognate constructions in closely related languages (English probably introduced it at some point in the last millennium. If so, it can't be a cognate). Assuming that it is more formal, your job is then to explain why similar constructions are not formal but rather come across as non-idiomatic. I am tempted to say ungrammatical even, but I am not sure about what goes wrong. I am experiencing some kind of processing or interpretative issue with the following 3:
a) Disse er bøkene mine. (you already rejected this one in #10)
b) Disse er to barn.
c) Disse er de fine maleriene hennes.
Pronounced with a neutral prosody, these make me squirm on the inside. If we put in
dette instead of
disse, then it is all fine. However, your examples are somewhat different in that they contain a following relative clause (
produkter som de kan lage..../ølstilar som har blitt...) and if you accept them as formal (but reject the three I provided), the rule you would have to postulate would perhaps be something like:
"If you want to be formal, you can have plural agreement in presentational constructions only if what is presented is modified by a relative clause. If it is not modified by a relative clause, plural agreement of this kind is not permissible."
The rule is cumbersome and seems like something that would be known only to the initiated of an exclusive society. That being said, having the relative clause there does improve my impression of them (just a tad) but I suspect that it is because relative clauses contain information that is compatible with contrastive focus readings (my post #11) and other things that are way too complicated for me. So summing up: on the surface there is a tight correspondence between English
these/those and Norwegian
disse/de but it's not a one-to-one mapping.
English
What are these/those?
These/those are my pictures.

Norwegian
Hva er disse/de?
Disse/de er bildene mine.

(just awful)