If the chance ever showed up to place more markings in the game, we'd gladly try to put some more in there, but when or if that time comes we cannot know at this point.
If we go to the idea at hand though, and let's say that we'd be able to just put the mass markings pack into the game there's still one thing I want to point out on that I personally don't agree with. Even though some markings might be good there, to my understanding the list of markings is huge compared to the original list or set of markings.
When in the character creator, the more markings that we eventually would put into the game, the harder it would become to navigate through the list of markings. I personally haven't spent much time using MM so I cannot tell to which extent it works this way, or how many of the markings should be considered "really good". But what I want to say is that only the best or possibly creative markings should be considered added into the game that work as "sets" if possible. Then also comes the whole thing with getting permission from all the marking creators to add the stuff into the game.
Some organization is needed and will always be needed. How many markings is it exactly inside of the Mass markings pack? To me it looks like if markings are going to be added to the game, either the scrolling or navigating through the markings list need to be modified a tad bit(Which is a bit unlikely to happen at this point), or only certain markings should be added.