[Medianext.MX]

Is that even allowed? Nexstar already owns CW and I thought you couldn't fully control two major US TV stations?

Well, the FCC rules stipulate any of the Big Four networks (ABC, CBS, NBC, Fox) can't be owned by a single company in the case one of these is sold, divested and/or merged with another one. This is what happened when Fox sold most of its media empire to Disney; they were forced to retain Fox, Fox News and Fox Sports because it overlapped with ABC, ABC News and ESPN on ABC.

variety.com 

Looking, however, at the history books: CBS/Viacom owned UPN during the latter years of its existence, simply because UPN was (technically) not a Big Four network; the Viacom/CBS merger in 1999 was also a factor in the FCC allowing legal local station duopolies later that year.

en.wikipedia.org 

The CW is, technically too, a non-Big Four network. So, if Nexstar can buy ABC, it would certainly not be outlawed. However, there are additional factors Nexstar might have in the long term: they operate 197 stations in 116 markets, and they would have problems in almost all of their markets if they get ABC (plus the O&Os). For example: in NY (WABC and WPIX), LA (KABC and KTLA), Chicago (WLS and WGN) and Philly (WPVI and WPHL), both ABC and CW O&Os are frequently in the first four spots in the news races (and in the general ratings), something that Nexstar would have to ask for a "public interest" waiver if needed to merge both stations. Additionally, you have WTVD and WNCN in the Triangle, that's two Big Four stations, and even worse, a real duopoly of CBS and NBC stations in Fresno, which, if they integrate the ABC O&O, would make an automatic triopoly (not allowed by the FCC, BTW), making a merger more difficult. To make things worse, Nexstar might have passed the FCC's market cap of 39% of TV households if it bought ABC's O&Os, leading to a through review of the deal if Nexstar planned to use warehousing to divest stations.