That's interesting. I did some grammaticality tests, and my conclusion is that they behave a lot like nouns, but with further restrictions. Like this:
| Sentence | a. "we're-better-than-you" (PAL) | b. "arrogant" (adj.) | c. "arrogance" (n.) |
|---|---|---|---|
| 1. Their [__] behaviour is annoying. | OK | OK | OK |
| 2. Their [__] is annoying | OK? | bad | OK |
| 3. They [__] fairly often | bad | bad | bad |
I'm not a native speaker, mind you. I feel like 2a ("Their we're-better-than-you is annoying.") is kind of passable? It doesn't sound as malformed as using 3a (trying to force the PAL into a verb position), but it sounds worse than 1a. I wonder if native speakers agree or disagree with this.
The text does mention Portuguese (my L1) also allows PALs, so I repeated the tests:
| Sentence | a. "somos-melhores-que-vocês" (PAL) | b. "arrogante" (adj.) | c. "arrogância" (n.) |
|---|---|---|---|
| 4. O comportamento [__] deles é irritante. | bad | OK | bad |
| 5. O comportamento de [__] deles é irritante. | OK | ? | OK |
| 6. (O/A) [__] deles é irritante. | OK (with "o") | bad | OK (with "a") |
| 7. Eles [__] constantemente. | bad | bad | bad |
4a sounds extremely broken, even if its English equivalent (1a) sounds OK. That makes sense if they're behaving like nouns - unlike English, Portuguese doesn't allow nouns to directly modify each other. I'd also probably give 5b a pass but, again, language specificities - it's easier to promote an adjective to a noun in Portuguese than in English.
Interesting share regardless of the above - thanks for sharing it!