Will Nextcloud support Chromebook users?
For example by providing an app and/or Chrome extension, allowing us working in the cloud.
I do look forward to replies, thanks in advance.
Best, Next
What should this app do? Only a bookmark or something more? 
I wonder if it could register as a source of contacts / calendars, without them being duplicated to the Google account, similar to on Android…
As an former ChromeOS user, I can say, that there is no contacts or calendar app 
…there are only Google Contacts and Google Calendar which can be used offline (in parts) … there is no way to implement CalDAV or CardDAV into ChromeOS natively.
sigh How very Google.
Unless you put your Chromebook in developer mode.
I think we talk about an end-user-solution which works in productive enviroments …However: Developer Mode itself has native CalDAV and CardDAV 