As interesting a notion as it may be, there's no way that "they" are a takeover invasion from WWE. It would make for very compelling television, and would be amazing if it could actually be pulled off without anyone knowing about it, but it would be the death of TNA as we know it. If Vince McMahon bought TNA, he'd likely do the same thing to it that he did to ECW and WCW, and we all know what that is. If there's any WWE component to "them," at most it's a faction of former WWE guys (Carlito, Helms, Knox, James, Burchill, Yang, Benjamin, Haas, whoever).
It's great because this angle really has people talking, and that's a really good thing. If they deliver. If they get people talking and speculating, get the anticipation of the wrestling world peaked, and then fall flat with another in a series of disappointments, that will be apocalyptic to them in my opinion. But if they can do something right for once, could be epic.
I wonder how many of the current TNA roster even knows at this stage of the game who "they" are. I wonder if they go into BFG with the only people knowing the identity of "them" being the guys directly involved. Even the guys who are directly associated with this angle could possibly be left unaware until the last minute. That way there's no mystery tweets, no slip-ups, no hints, nothing that could spoil the revelation that will chart the course of TNA for the upcoming months. If it were to be something as significant as a WWE takeover (which again I think has 0% chance of happening), and everyone knew it, it would be nearly impossible to keep it under wraps. The TNA guys would have to see their ultimate demise from an angle of this nature, hard to imagine they'd keep quiet about it.
Personally I think "they" will be a mixture of a few elements. I see three or four guys from the current TNA roster being joined by a backstage character and one debuting new person. I think it will be Mr. Anderson, joined by Abyss and a couple of old guys (Hogan, Bischoff, Sting, Nash, I'm not sure who, but a couple of these guys). Throw Russo into the mix as well as some former WWE reject (Helms for example) and there you have it. Probably disappointing in the end, only time will tell.
I have to say, though, I do find WWE's references to Mick Foley on RAW and SD!, his interview with Joey Styles on wwe.com, and references to "Countdown to Lockdown" surprising and a little intriguing. It likely means nothing, but flies in the face of everything Vince McMahon has ever said and done regarding anything non-WWE in the past. Hard to imagine that he acknowledges nothing outside of the WWE universe for years, but then all of a sudden has such a soft spot for Foley and his book at this point in time. Especially when Foley jumped ship and has been somewhat vocal in his displeasure with Vince and the WWE, directly or indirectly via EV2.0. I would think Vince if anything would be pissed off with Foley rather than respectful of him and helping him promote himself.