From the F/E thread:
XSEED has registered a Fate/Extella domain:
http://www.fateextella.com/
Remaining unknown domains from XSEED:
b _ _ _ _ _ i.com
s _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ s.com
t _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ y.com