Re: Outlook and SharePoint?
You just don't grok it at all, do you? Let's look at your post:
" their auto-upgraded (strictly no choice) mail client and collaborative filesystem"
What mail client and collaborative software will they be using in future? It doesn't say in TFA. You seem to be making some assumption not in evidence, including that auto-upgrades can't be blocked at the firewall.
"start to methodically stuff LibreOffice integration in carefully-crafted-to-be-unfathomable ways?"
You seem to be assuming that whatever they use would do that. Again, no evidence that it would or even that they'd choose something that would.
Remember they're doing this to get away from any dependency on Microsoft online services so you can discount Exchange and if you discount Exchange then you can probably also discount Outlook because there'd be no reason to retain it, especially, given, as you point out, this is subject to upgrades from Microsoft.