Will there ever be such a feature ?It might be nice when you're able to update
frequently 
changing web sites that remove old content and you want to 
access both old and new data.

On the other hand, this could be a bit of a complex 
feature... but maybe HTTrack could make use of an existing 
VCS to provide such a thing.
Then it would also be necessary to provide links to the 
versioned pages from the index.html.

Sure, it's possible to just brute-force-copy the whole site 
each time before the next update, but that can be a waste 
of disk space.

Well, just an idea.