Are there plans to include a replacement for MS Outlook in LibreOffice? I know it’s a platform-specific question, but if one of the aims is to supplant MS Office, then leaving Outlook behind means the office suite will still be there, and probably the other elements of Office would be used?!
I don’t think that LibreOffice will ever ship an e-mail client. Why? Because there are plenty of open-source e-mail program and user is free to choose from and also more and more cloud e-mail solutions exists e.g. gmail, yahoo-mail, hotmail etc.
I use Mozilla Thunderbird: https://www.mozilla.org/en-US/thunderbird/ for years and it does everything I need.
Searching the web and I found several links like:
Comparison of email clients - Wikipedia
I don’t think that there are any current plans to include an email client in the LibreOffice suite.
You may associate an email client with LibreOffice, if you like. See these questions for more details:
If you aren’t tied to MS Exchange server, then use Mozilla Thunderbird. If you are, take @qubit1’s advice about Evolution.