We currently do not have any public roadmaps we do share.
We’re, as far as I’m aware, not planning to implement properietary solutions like e.g. ActiveSync.
As for email communication we do focus on IMAP and SMTP at the moment, because that’s the broadest used protocolls amoung our users.
Regarding xOauth I have been answering on the linked thread that we have it on our list ( End of support for Basic Authentication access Office365 ).
Just because you can’t find any marketing on a news page, it doesn’t mean that a project has died, doesn’t move or get any updates. You can clearly see the oposite on our release news and commit histories.
Zammad is supposed to be simply, powerfull, but still simple. We don’t plan to grow in an OTRS like state where you need several days for a configuration. That’s not helping and not our goal. You will always find corners where Zammad doesn’t fullfill your needs I guess.
If you want to use Zammad and still can’t work without a specific feature, you can always contact our sales team for a custom development.