We have announced that we will bedeprecating the Exchange Online In-Place Discovery and Hold functionality in the future (though the time is currently unspecified) and are recommending customers use the Security & Compliance Center to create and manage eDiscovery and content searches.  For customers that have a large investment in the legacy In-Place eDiscovery and Holds feature and want to preserve their functionality and access and start adopting the Security & Compliance Center eDiscovery search interface, I have created a script that will export the mailbox searches (Get-MailboxSearch) and recreate the searches as eDiscovery cases.

I've put together a blog with more details as well: https://www.undocumented-features.com/2019/01/10/migrating-from-exchange-online-ediscovery-and-in-place-hold-to-the-security-compliance-center/

UPDATES:

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<#  
.SYNOPSIS 
Migrate Exchange Admin Center In-Place Hold Search to Security & Compliance Center 
Cases 
 
.PARAMETER AddCreatedByToEDiscoveryManagers 
Add the user listed in the CreatedBy parameter of the original mailbox search 
to the eDiscoveryManager role group. 
 
.PARAMETER Credential 
A credential object. If not present, you will be promtped. 
 
.PARAMETER Debug 
Enable debug logging. 
 
.PARAMETER Logfile 
Does just what you think it does. 
#>