Apple Software Manager Craig Federighiexplained in an email to a user that the company is working to add APFS file system support for teams adding Fusion Drive.
APFS replaces Mac OS Plus (HFS +) as the default file system for hard drives (SSD) and other flash storage devices, but for computers with Fusion Drive disc system does not currently support this format and Apple would be close to announcing its compatibility very soon according to Federighi to the user who asked the question.
WWDC possible date to announce compatibility
It all fits in the minds of Apple users right now and it is that the close date of the Apple Worldwide Developers Conference, which already has exact start date and time, could be the perfect time to announce the compatibility of this file system with Macs that mount Fusion Drive. Federighi's response to Jonathan (the user who sent him the email) has been published in the MacRumors medium:
Hi Jonathan,
We intend to address this issue very soon ...
Thank you,
-Craig
It may be possible to solve this on June 4, the date on which the event keynote is offered and Apple shows the news of the next version of your operating systems, macOS, iOS, watchOS and tvOS. In any case, it is important that Apple solve the compatibility of these computers with the new file system launched last year 206 for iOS users and later in 2017, for Mac users.