> Will there ever be such a feature ?
Well, the problem is that this is simply not possible with 
the HTTP protocol. I could emulate such thing by handling 
multiple revisions, but it is way far too complex for a 
program like httrack.

The best solution IMHO:
- put your "My Websites" on a real CVS system
- update the site(s)
- do a "cvs commit" to commit changes

In this was the revisions will be automatically handled.