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Well, not entirely.
First, the tool I'm using for backups doesn't handle XZ AFAIK, but that's irrelevant. Secondly LZIP offers recovery mechanisms (lziprecover).
See e.g. http://my.opera.com/ruario/blog/2013/01/15/faster-xz-compression#comment102565842 and follow-up comments.
I don't want to start off a discussion of which format or algorithm is 'the best'.
LZIP exists though, and many persons are using it. Hence, I was just wondering whether you're considering adding LZIP support to the 7-Zip program - it would make 7-Zip even better and more complete.
Since an open source LZIP library is at hand already, I assume decompression wouldn't take months of programming to implement.