in a hybrid exchange environment the autodiscover entry directs to the OnPrem exchange servers.
To use a hybrid exchange environment i only need to publish the exchange agains the EO and EOP IP´s. When i want to access the Exchange from an external client without access to the AD SCP Entrys i need autodiscover.
There is a new version of autodiscover (v2) which is not well documentated or not finalized yet, but as far as i see modern clients go to o365 first in every case with this version of autodiscover. If a mailbox is not available in o365 EO directs my client to Exchange OnPrem.
This assumptions lead me to my question: Is it further needed to publish the OnPrem Exchange via .../autodiscover for full client functionality? I
Autodiscoverv2 is documented, and yes is contains 'shortcuts' when your mailbox is hosted in the service (for recent Outlook versions). However, please do implement Autodiscover records properly to prevent issues or non-functioning feats, such as federation with partners (when applicable) or co-existence features (F/B between on-prem/365 mailboxes), integration with teams (eg calendar lookups to on-prem mailboxes), etc. That said, when all mailboxes are residing in Office 365, you can opt to configure the autodiscover endpoint to point to Office 365 (autodiscover-s.outlook.com).
you can set up Hybrid, HCW will show two errors, Unable to create an Org relationship and unable to create migration endpoints. Without Org Relationship you will not be able to set up Cross-premises Free Busy. You can create Migration Endpoints in O365 Portal later by pointing it to your CAS server.