Ok, this seems to be much more tar-compatible...and output to stdout
could be filtered or somehow handled...
But the main Problem is that 7z is a format similar to the classic zip
fromat and thus not streamable, thats more a problem which possibly
could only be bypassed by developing a streamable version of the algorithm.
But Maybe I'm wrong because I'm not very familiar with all that stuff...
This example is from the p7zip README file:
tar cf - directory | 7za a -si directory.tar.7z
So it seems streams are supported.