If you install waydroid-settings instead of waydroid-runner, you can have Android run in the background. It could then be started/stopped from a menu entry in Sailfish Settings, like AlienDalvik.
You could open individual apps directly from Sailfish app grid. But, be advised that waydroid multi-window option doesn’t work in Sailfish, so you can only see one app (better said android window) open. Well of course you can open the Waydroid Full UI and use as an Android phone like it is now. Another catch is that it is not possible to open the same app consecutively after it is closed, the window wouldn’t appear.
i.e. open Whatsapp → close it → open Whatsapp again fails. Will have to open some other app before you open Whatsapp again.