for Deviation and [link]
for the comment
Matt Frank states in his Godzilla Rulers of Earth issue 2 deviation that all incarnations of the 1998 creatures will forever be called ZILLA. In addition to the 1998 creature's trademark and logos being CANCELLED and ABANDONED, this comment by Matt himself (who is working with Toho and is friends with them), it would be more than safe to say that the name change is completely official (maybe the 1998 creature's DVD will say Godzilla forever, but it's now official that it will forever be called ZILLA from 2004 and onwards).
To see more legal stuff saying that the name change is official, go to my other deviation:[link]
And go to Wikizilla's thread on the name change:[link]
Thanks and make sure you read everything that those links say.