From my statistics, this post is completely off base...
Feel free to correct me if I am wrong - but my scans of the zone file give completely different results.
There are a total of 10,000,000 7Ns.
As of 1/4/16
Total-----Registered-----Reg %-----Remaining-----Rem %
10,000,000-----1,205,399-----12.05%-----8,794,601-----87.95%
There are a total of 2,097,152 7Ns without a 0 or a 4
As of 1/4/16
Total-----Registered-----Reg %-----Remaining-----Rem %
2,097,152-----988,097-----47.12%-----1,109,055-----52.88%
***Keep in mind that about 1-2% more domains are registered than noted here.
This report was pulled from the zone file which exempts any domains without nameservers. Which as best as I can tell runs about a 1-2% average.