[see epic for more details; TL;DR: dtors of polymophic classes need to be out-of-line]

Most classes defined in the file have no out-of-line dtor, so are prone to -Wweak-vtable. It's private API, that's why it's not critical, but it's code hygiene that we should eventually implement.

As an aside: the template subclasses of polymorphic classes are quite heavyweight constructs. If they're used more than a few dozen times, they should eventually be de-virtualized (cf. QSlotObject or QGenericRunnable for how).