Bernhard,
Currently VMWare 6.7 is slated to be supported in MiCollab 8.1 SP1 towards the latter part of this month. However, it is important to state that the project has NOT locked in content yet. Therefore it is always possible that support for VMWare 6.7 could be moved out.
Also, just to be aware (according to information I have gathered from the Internet): If you’re using vSphere 6.5 Update 2, you can’t upgrade to 6.7 yet. There’s no supported upgrade path between the two hypervisors because update 2 was released after 6.7.
• This is a VMWare issue not a Mitel Issue
The short answer is that I would defer if possible as currently Mitel is only supporting up to VMware Release 6.5.