I guess that's the "problem" with generic product names. There's also Apple Calendar, Google Calendar, Microsoft Calendar etc. - Docs is not different than that.
If you say "open Calendar", I don't know if you mean Apple or Google or Microsoft. If you say "open Docs", I know it's Google and only Google.
This is no different than if the project called itself "Word", which would be equally confusing with Microsoft.
Neither Docs nor Word are genericized. They're both totally valid trademarks. Which is why naming this project "Docs" would be immediately shut down if any private organization tried it. And I've never heard of governments infringing private trademarks before, so I'm curious what's going on here.
Same with Books. It could be Google Books, Facebook, or Open Books.
No, they couldn't. That's why there isn't any Open Docs or Libre Word word processor.
That's very specifically why it's Libre Writer. Why it's FreeOffice TextMaker. Why it's FocusWriter and Writemonkey and whatever else.
A major part of trademark law is likelihood of confusion. Both Docs and Word are associated so strongly with Google and Microsoft, that a judge is almost certainly going to side with them if you try to call your new word processor Docs or Word.
And there's also AbiWord, which is still under active development.
Or speaking of which, all the gazillion office suites with Office in the name.
And "office" became the term for an office suite, the way "calendar" and "contacts" and "word processor" are just descriptive terms too.
But "Docs" and "Word" have a clear, obvious distinctiveness that "office" and "calendar" don't. "Word" and "Docs" don't inherently mean "word processor". Heck, OpenDocs.com is for legal forms, not word processing.
I really don't know what you're arguing. Go ahead, start a word processor named just "[Company name] Word" with the space and get sued by Microsoft and lose. You don't really think you'll win, do you? This is not a controversial or blurry area of trademark law.