I don't think the delayed release has anything to do with GW waiting so that Nintendo can't "block" emunand. In -most- cases when Nintendo releases a new firmware, the files are changed enough so that the locations of the patches that need to be made are different which crashes the loader. It's not that Nintendo actively seeks to stop GW with every firmware, it just naturally does it when the code changes. Whether GW releases now or later, Nintendo will or won't release a FW that tries to block it, so it doesn't really matter on that front.
My best guess is they are waiting until they can get their hands on a US N3DS so they can find the proper permissions to patch and release everything all at once so there aren't a bunch of different GW firmwares running around causing confusion. If I had to put money down, I would expect release no less than 2 weeks before launch (about the time when they may feasibly be able to get their hands on a non-ambassador US N3DS and create the proper Launcher.dat for it).
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