The newest Fantastic Beasts film was thrown into upheaval just as production was getting underway when Warner Bros. decided to cut ties with Johnny Depp, who had previously played the big bad Grindelwald. While a delay in release for the film gave the studio more time to find a replacement, there was clearly an interest in finding a new actor quickly. A report dropped shortly after the news that Depp was gone that Warner Bros. was talking to Mads Mikkelsen about taking over the role. However, Mikkelsen himself seems to be indicating he doesn't know anything about it.
The Rogue One actor recently spoke to IGN and he referred to the recent reports of him taking over the Fantastic Beasts role from Johnny Depp simply as "rumor." It seems that he's claiming he doesn't know anything more than we do about him becoming the new Grindelwald. According to Mikkelsen...
Oh, that is on the rumor basis as we speak. So I know as much as you do from the newspapers. So I'm waiting for that phone call.
Mads Mikkelsen is clearly keeping things close to the vest here. If we parse his comment one way, he could be confirming that talks are indeed taking place, that is after all what it says in the "newspapers." Of course, if talks are still ongoing, as seems to be the case, you rarely hear one side or the other confirm that, as talks always have the potential of breaking down. What Mikkelsen is clearly not doing here is conforming that he will in fact become Grindelwald. While it could happen, the deal at the very least isn't done.
It's also possible that Mads Mikkelsen's name came out early and while Warner Bros. wants him for the movie, the talks hadn't actually begun yet. When the actor says he's waiting for the phone call, he could mean that quite literally, that nobody has approached him yet, but that based on seeing the same report that we all did, he's expecting that call to come very soon.
According to a public statement by Johnny Depp himself, Warner Bros. asked him to leave Fantastic Beasts 3, following the result of a libel lawsuit he had brought which did not end in his favor. According to reports, WB parent company AT&T may have been put its foot down at that point. He had reportedly filmed a single scene of the new movie before walking away.
While there are certainly many interesting potential actors who could take over from Johnny Depp, Mads Mikkelsen is certainly an interesting one who has experience playing some pretty stylish villains. He would almost certainly bring something interesting to the role. We'll have to wait and see if this actually happens. If Mads Mikkelsen's phone still hasn't rung yet, it probably will very soon.