You can now move users from Skype onprem directly to teamsonly but you need CU8 for Skype
When you do this the MMS will trigger and migration your Skype meeting to a teams meeting
The Meeting Migration Service (MMS) is service that updates a user’s existing meetings in the following scenarios:
- When a user is migrated from on-premises to the cloud (whether to Skype for Business Online or to TeamsOnly).
- When an admin makes a change to the user’s audio conferencing settings
- When an online user is upgraded to Teams only, or when a user’s mode in TeamsUpgradePolicy is set to SfBwithTeamsCollabAndMeetings
- When you use PowerShell