Now on to the point of this thread, if they made Rank B elite monsters available inside dungeons it would allow everyone to spread out on different contents on the game. They could place these Rank B's like that beast above, it'll give players that extra and optional approach to a dungeon and make the experience a little more diverse. I know that Hunts were supposed to be exclusive to open world content but as mentioned above, this feature isn't really meant for a game like this. So it all comes down to "Why not?" It'll give back that importance of running those dungeons while keeping the importance of hunts to open world (Rank A's & S's).

cont.