Prepatch isnt gonna happen on the 29th. Too many things going on in WoW for that to be prepatch day. And the last nail to drive that home is server merges on the 29th. No way are they gonna do pre-patch on a server merge day, with the same servers that already had problems very recently.
More likely october 6th will be pre-patch, maybe october 13th making it the smallest pre-patch. Or my guess (or what I hope for) it will be delayed all together, because there are so many things not even finished in beta and I doubt they want pre-patch to drag on. Survival hunters zero changes, monk not a single blue post and so much of the monk class is broken…content just broken and not even there. No way can it be released in the state it is, and with so many classes broken with no feedback at all from the devs, if it does it will be the most broken expansion launch in history of WoW.