Personally, I think this is another one of those 'elitist' things. Even if you ask for reiki lineage, it can be so easily faked and how often will someone actually go and check up on said lineage.
I don't feel its important to know lineage, I am more interested in learning (and teaching) HOW to do reiki, not who taught me or who taught you etc
I think the focus should be on the Reiki itself and passing it on to as many as possible, because the more people capable of doing reiki, the better for the world......