This is a great article if you're interested in Star Wars, Marvel, or just the entertainment industry in general.
Here's some choice bits discussing never-ending movie series:
That wreaks havoc on beginnings, middles, and endings. No one ever makes a true act three. The universe never ends, really. It ebbs and flows from individual, single-character-focused movies through big Avengers denouements. The quantum realm in Ant-Man sets up the mystical world of Doctor Strange. The alien nature of Asgard in Thor sets up the science fiction of Guardians of the Galaxy.
And quoting Episode VIII director, Gareth Evans:
We all have to be careful of the Who Wants to Be a Millionaire trap. When that show premiered and was once a week, all I wanted to do was tune in. The minute they changed it to five days a week, it seemed a lot less special. Let’s not flood the market.
This is the shared universes’ shared Ragnarök—dozens of movies with impenetrable interconnectivity floating amid a sea of unending remakes, reboots, rewarmings. For those of us with emotional investments in these characters and these worlds, that would be heartbreaking, like the commercial in which Fred Astaire dances with a vacuum cleaner.
I find Marvel movies exhausting because of this. I can't make myself care about any one movie, character, or story because the burden of caring about the entire series gets in the way.
I don't want this to happen to Star Wars. Nobody does. Here's the potential remedy:
In comic books, superhero universes survive in part because of what Stan Lee famously called “the illusion of change.” The status quo looks like it’s constantly evolving, because our hero defeats the latest threat, but really everything just resets to zero. Time, in comics, stands still.
But in the Star Wars universe, time moves. Han Solo, Princess Leia, Luke Skywalker, and the legacy actors playing them can grow from callow youth to wise old age and then pass the torch.