I kind of understand where people are coming from with this, it would be cool for Darth Vader to show up for more than 2 scenes and actually get to do something, but I don’t think they’d really be able to sustain it for an extended period of time. If there is one thing that is consistent in the Star Wars TV Shows and Movies, it is that Darth Vader is used sparingly. He only shows up for a total of 37 minutes in the original trilogy, he gets around 10 minutes in A New Hope, 13 minutes in Empire, and around 14 in Return. In Revenge he only gets 2 scenes, he only appears for one scene in Rouge One, we get the epilogue scene in The Clone Wars which is only around 2 minutes, and he only appears in 3-4 episodes of Rebels for a grand total of 10 minutes. He gets 22 minutes in Obi-Wan, but that shows around 4 and a half hours long so it’s technically consistent with previous entries. I actually really like that because too much Vader I think would not work that well. Sure there have been comics and books where he’s the main character and focus of the story, and there’s a chance it could be cool, but I just don’t think it would satisfy anyone.