You're gonna have to pry it out of AT&T's dead hands if you seriously want Comcast to acquire DC Comics. Like Disney's Marvel Entertainment, DC Comics is owned by DC Entertainment, a subsidiary of Warner Bros, whose parent company is AT&T. Also, AT&T (which is the most powerful ISP like Comcast) is pretty much new to the entertainment world after last month's merger success so they might try and revamp DCEU in the long run. As you said, it's not gonna fly in any other way, considering WB's past success of DC Comics movies, especially Wonder Woman is a hit last year among fans and critics. They might have a few struggles there, but having DC Comics for WB is the only way to arm themselves against Marvel Comics movies from Disney, Sony, or Fox. WB is as much as a serious competitor in the entertainment arena right next to Disney, they ain't gonna bargain, especially they have the backing of AT&T.
As long you don't remove Marvel Super Hero Island within IOA, then it's totally legal to have DC Comics area within the same park or in the 3rd theme park as well, if you bother to have more room. However, it makes no sense to have two competing superhero comics brand in the same park so it's unlikely gonna happen, since removing MSHI in favor of the DC area would end Universal's theme park right with Marvel, as we know it, and Walt Disney World would have a free reign of using whatever Marvel properties as well as the Marvel name in its parks (which also means Disneyland Resort can use the name as well). Comcast isn't gonna let that happen, especially how fiercely they try to become the next Disney of the century.