As the sharing of courses will be a proof-of-concept, account creation/grade transfer could be done manually at the beginning (Q1 2020).
Later maybe it would make sense to use OAuth or alternatively eduroom logins.
> the community hub functionality will also be cancelled soon or within the next years?
> MoodleNet is designed to replace that, yes. Including (most importantly) the sharing and curation of entire Moodle courses...
The problem is that we should have a first running prototype soon and a production-ready site Q3 2019. So I am afraid that Project MoodleNet will be in a too early stage at that time.
Does it make sense to still rely on the community hub functionality?
At least the publishing part? So then we could also implement our own front-end client for the central listing of published courses. We just needed the respective web-services API.
The publishing part (in Moodle) should be fine. It's the hub that is no longer supported.
However, that kind of sharing doesn't give you very much - it effectively just posts links with some metadata to a central place. Any user that wants to go to a course on another site will still have to log in there etc so you'd need to organise OAuth or something as you said, more manually.