There have been two things which point to this frame of thinking
Arena and Rated Battleground Season 10 is scheduled to end as early as November 15. At that point we will determine who is eligible for the end-of-season rewards, a process that should take approximately one week. It's very important for players who feel that they may be eligible for Arena titles and/or the Vicious Gladiator’s Twilight Drake to refrain from transferring their characters to another realm or faction until after Season 10 ends. During the break between seasons, all Rated Battleground and Arena matches will be unavailable.
First off if the PTR is already on the release and we know the current build has minimal changes this points to 4.3 being at minimum a week Tuesday. In addition the End of the PvP season points even more so to this going right out and saying that November 15th could be the earliest date the season ends. As we know 1 week after a season ends the new one begins and this means a new major content patch is upon us. So with all these things in place we could see 4.3 as early as November 22. I am not sold completely on November 22nd though as I believe American Thanksgiving is the 24th and that would mean they are forcing competitive guilds to play during holidays something which over the years they have always tried to avoid. Doesn't mean they won't do it, just means they haven't done it before. Some would say it is not because of competitive guilds, but because Blizzard employees won't be around to apply hotfixes. Either way I don't think it seems very likely, and November 29th seems much more likely, but only time will tell.
Also with Blizzard doing this they are allowing that Star Wars game you may have heard of coming out on Dec 20th its own date. Something in the past they have always tried to avoid and have released something to mess with other competing games release dates. Again there is a first time for everything. Regardless of what day it is 4.3 will be out soon so time to prepare is upon us.