http://www.gog.com/forum/gabriel_kni...y_likely/page1
http://www.telltalegames.com/forums/...ad.php?t=33854
The rumors with the GK thing is, that she was thinking about making HD remakes of all three games. Apparently number 2 would be completely redone in a traditional style, replacing the FMV, so they could go back and rerecord the voice actors for GK, get Tim Curry.
Remakes are slightly different situation than an all new game. Think how Lucasarts & Gilbert's company worked on Remakes of Monkey Island I and II, while Telltale worked on Tales of Monkey Island (the all new 'game' in the series).
Of course Lucasarts (now under Disney management) is a different entity than Activision, and may choose to do things differently. But then again we don't know much of anything on how Activision chooses to do things. They haven't even done anything yet, except rerelease the games through GOG and Steam.
As for the Sierra multi-license, it seems based on the various reports that hint about it mainly focused on the various Quest series at first (they apparently hinted specifically at Space Quest and Quest For Glory after King's Quest). That still doesn't mean they didn't have access to GK or not. But we will simply never know.
As for 'multiple game licenses'? Who knows... Activision was working on its own Walking Dead FPS action game, around the same time Telltale was in the middle of making its Walking Dead 'adventure' game. Telltale was given a license renewal to do Season 2. But the company that owns the Walking Dead franchise is the one who can make those kind of decisions on who gets to use the licenses and how.