So I did retrospectively upgrade to APFS on an 13" MacBook Pro with Retina display (Early 2015). I'll list the steps I've taken but I'm not really sure why this ultimately worked:
1. Turn off filevault and wait for decryption to finish.
2. From recovery select the option reinstall High Sierra (with the APFS checkbox selected).
3. Let the process finish and restart until the the kernal panic or failure to install message shows up.
4. Restart holding ⌘ + R to re-enter recovery and select disk utility.
5. partition all remaining freespace to a new volume (this will hangup with an unending beach ball).
6. Once the windows freeze with only curser freely moveable force shut down by holding the power button.
8. Start up again by holding ⌘ + R (if you start up and get a wonky 'internet recovery' screen: force shut down again holding the power button).
9. Once in the High Sierra recovery go to disk utility and run first-aid on the HD (this takes a little longer than I've expereinced with first-aid).
10. Once first-aid is complete select the HD and from the menu bar select edit followed by convert to APFS. This should now complete successfully.
11. Close disk utility and once again select reinstall High Sierra (this time there should be no APFS checkbox due to already being APFS).
12. Let the installer complete and login as normal.
Now once again, I'm not sure why this all worked and maybe someone with a little more knowledge could lend some inforamtion. This however resulted in no dataloss or uninstallation of current applications or settings.
http://imgur.com/a/oVQX5