[Development] QFileSystemWatcher and Recursive Monitoring

[logic.cpp]

So how about something like this (others have suggested something along these lines):

In order to work recursively, the file-system watcher class will require the user to implement a sort of snapshotting "backend" which will be interfaced/used for FS change comparisons. And only as a "bonus", the class will also offer a default such backend on applicable OSs (i.e. all except Mac<=Snow Leopard, which in fact don't even need any snapshotting at all).

I think this wins because first off, it makes things nice & easy for applications that DO involve FS snapshotting /anyway/ (which is possibly 70% of all use-cases that need recursive monitoring in the first place) you could simply interface your application's snapshotting functionalities straight into Qt's filesystem monitor! This is interesting for ALL OSs even those that already offer granular file change details.
And at the same time, it's very clear to users of this class that recursive monitoring must have snapshotting - unless a default is kindly provided by Qt BUT not on all OSs.

So in other words the question is:
Is it acceptable for Qt to say "Hey look; to use my QFoo facilities, you must implement <bar> on your end and plug it in to QFoo. Y'know - most use-cases QFoo was designed for have implemented a <bar> of their own anyway. But just because I'm so nice, I'll offer you a default <bar> implementation wherever I can" ?