Six years is a short time; moreover, it would be a poor strategy for the Big XII to sit by and do nothing, while watching the SEC, the BigTen, and the Pac-12 increase their stature and their market worth, simply because Big XII members are locked in for six years. That is simply begging them to bolt at the end of that term.
If the Big XII does not want to go the way for the Big East and/or the SEC, it had better make hay while the sun is high. Taking teams from the ACC now certainly cuts into the short term revenues for the schools currently in the Big XII; however, I have yet to see a compelling argument as to why it would not serve their long-term interests (even for Texas).
Texas knows that whatever happens it's one of the only few in that league guaranteed to find a safe-landing place in another conference. It's why they're so much more forward about only caring *about the here and *now as well as getting more benefit and say in conference moves and transactions. Bringing more people to the pie without actually making the pie properly, proportionately larger only results Texas making relatively less money and having less of a say in conference matters as a result of so many siblings. While OU might or might not mind something that, it's something Texas definitely would not want...especially going down to somewhere along the lines to just greater than 1/16th of the vote.
And also just jumping up from 10-16 teams is a huge move for a conference to digest, especially all at once. And without the NCAA passing a new rule allowing pods, extra semi-final games, etc, all these teams are still forced to play in a 2 divisional setup...with maybe at best something like the rotational mess of a setup that the WAC used prior to the MWC members splitting off.
All this strategy seems to be is overloading the conference because you're afraid more teams are going to be poached based on the last offseason...or that stability really isn't the aim here and you think the Big 12 needs to try to take some attempted big action to eclipse the other conferences (PAC, Big 10, SEC)... But if so, at this current moment, it's not the proper way of accomplishing such.
WVU has no loyalty to the Big XII and is easy picking for expansion; moreover, the travel costs for their Athletic Department are huge in the Big XII.
Where else would they possibly go? No one else wanted them. They tried to speak to both the SEC and the ACC about a conference move and each (because of the school not bringing much more market, and - among other things - it's just terrible standings academically) kindly told them to take a hike. Neither conference wanted them then and neither would want them now.*
Plus they got out of a dying Big East and into a big conference; they're nothing but content right now, even if they were just invited as a stop gap team and even with the travel distance. Would they have rather been in the SEC or ACC? Probably, those were their first choices. However, neither conference wanted them.
K-State's 2012 season has made them very attractive to the BigTen. Moving to the BigTen would renew their rivalry with Nebraska (who is their historical rival, not KU).
...no it hasn't. 1-2 good years doesn't suddenly make anyone an attractive commodity (see West Virginia). Throw in the fact that they're quite small market - nothing much is brought to the table - (and perhaps more importantly) also not an AAU school; there's very little chance the Big Ten is all that interested in them.*
Even if the Big Ten were to decide to take a more risky, Rutgers-esque endeavor, *looking for a quick small addition to balance out a larger one...with both pretty much in the same place (and one not bringing terribly much more than the other), it'd be more likely to see them end up going after KU with AAU status than KSU (and neither of those are really all that likely at the moment)
Teams aren't just added to conferences because they're currently playing well that season.
OU is attractive to the SEC.
Except OU wants to have nothing to do with the SEC or the possibility of joining it; they've made that well clear in the past (along the lines of they look down at the conference / feel it wouldn't help - possibly impair - their university's image)
The schools in the Big XII that are not attractive to other conferences are KU and Iowa State (unless the BigTen pulls them in simply to grab K-State), and Texas Tech. All of the other schools will be entertained by other conferences, if not now, then in five years, when the money is about to run out.
(I can't see them making any sort of move towards Iowa State...at all; also Texas Tech most likely has wherever Texas goes...if the PAC-12 talks with Texas that fell through are of any indication, Texas plans on bringing Texas Tech along like baggage wherever they go...you also left out Baylor on your list of "left behind" schools, but KU, Iowa State, and KSU would also all likely be on that list with them)