As for the devices that will be affected (in a positive manner here), they happen to be the Sony Xperia Z3+, Sony Xperia Z4 Tablet, Sony Xperia C4, Sony Xperia C5 Ultra, Sony Xperia M4 Aqua, and Sony Xperia M5. So far, all of the support pages for the listed devices show Android 6.0 Marshmallow as the next version of the mobile operating system that they will receive, despite the fact that right now, they are rocking to Android 5.0 Lollipop.
Taking into consideration that Android 6.0 Marshmallow is already up and running, this makes perfect sense. Sony no longer needs to spend time working on the Android 5.1.1 update, where they can now jump to Android 6.0 Marshmallow. As to when this will happen, it remains to be seen, but this year might seem to be rather optimistic.