High Sierra & Fusion Drives

When will Apple update MacOS High Sierra so that the new file system will work with a Fusion Drive?

I know that High Sierra works well with a Fusion Drive (as it's doing on my iMac right now), but that the old file system can't be converted to the new, more secure, efficient file system yet on a Fusion Drive.

I plan to buy a new iMac, and love the affordability of the Fusion Drive. But I don't want to buy one with a Fusion Drive if High Sierra won't eventually be updated so that the new file system will work with a Fusion Drive.