> will the new cache format also support 
selective 'removals' 
> from the cache to redownload a single file?
You mean to force the redownload of a single file?
Windows: 
Just double click on the cache.zip and remove desired files 
in WinZip

Linux/Unix: 
zip -d foo.zip <http://www.example.com/badfile.html>

To extract original data:

Windows: 
Just double click on the cache.zip and extract desired files

Linux/Unix:
unzip foo.zip