The time is about right to have a testing medium available. First a couple of items need to be done before testing is worthwhile. The initial ISO will be fairly sparse of configuration changes and is for testing changes that would improve the experience. Not for resale or installation.
Work will start after next sync and KF5 5.39 release
 QT 5.9.2
 KF5 5.39 (add qqc2-desktop-style)
 Plasma 5.11 (add plasma-vault and drkonqi)
 KDE Apps 17.08.2
 Push a couple of app updates after full stack rebuild sddm/partitionmanager