I'm working on finishing a story that's written in first person, entirely from the PoV of the main protagonist. As I near the end, I am organically thinking of ideas for a hypothetical sequel, and one of those ideas is keeping the first person perspective BUT having the story be written from multiple characters' PoVs besides the first story's main protagonist. Although I was tempted to write my current story from multiple PoVs, sticking just to the main protagonist felt appropriate due to how it was also functioning as a coming of age story. But the sequel I've been thinking about would be more suited for multiple PoVs, as characters from the first book will find themselves separated by both duty and circumstance, with each focused on their own unique issues that were a result of the fallout of the first story - all equally important and deserving of attention for the sake of what the sequel wants to do. Now, I've read novels where it's written in first person perspective but switches between different characters each chapter, so I know it's 100% doable, but my worry is that it would feel disjointed from the first book since the first book never hopped between characters' heads. Even though I have not made any commitment to writing a sequel, I still am curious what everyone else thinks about this. Would it put off a reader? Or would it be accepted as a natural progression of what the story between two books is trying to accomplish?
I've got an extended series where I do that. Each of the four trilogies has a single main-character POV and a secondary POV per book. You get the same person for three books and then three separate people's perspectives. It will wind up being four main POVs and ten secondaries, I think since two of them appear twice.
Ken Kesey wrote Sometimes a Great Notion using multiple POV, I think as many as 7. One of my favorite books, I recommended it often, some found it hard to read, others really got into it and loved the book as well. The switching is tough to pull off smoothly, I would recommend picking it up and see how he did it. I can think of no other author who attempted it to the degree he tried and was successful at it.
In my case, it's not so much the switching between characters in first person that gives me pause (as I said, I've read books where it worked, with each chapter being one character), it's the fact that my first story is entirely from one character's PoV, and my idea for a sequel not sticking to just that one character.
I've not read Sometimes a Great Notion, but the example I think of that pulled it off well is Game of Thrones. No idea how my POV's he uses in that series, but I know it was a lot! I'm pretty sure the Divergent series does this (I can't remember if they introduce the second POV in book 2 or 3), and it worked fine in my opinion.
I don't think I've ever seen this done before. There are series like GoT that have multiple POVs throughout, and there are series that switch the POV character between books but still stick to one at a time, but I can't think of any examples like yours. That doesn't mean it can't be done, though. Like most things in writing, it will all come down to your execution. The closest example I can come up with is NK Jemisen's Inheritance trilogy. She doesn't switch from single to multiple POV, but the second book is still radically different from the first in terms of setting, characters, tone, and story. And it was jarring at first, but she drew me in with a good story that continued the story from the first book in an unexpected and magical way. I don't see why your structural change couldn't work just as well. If your readers liked the first book well enough to pick up the second, they'll probably trust you enough to keep reading past their initial surprise.
I can't really can't see it being a problem. If I'm understanding you right, the characters we're going to hear from in book 2 have gone through changes, growth, whatever, similar to the MC in book 1 and now we'll see how they deal with their new responsibilities, etc? Sounds great. Seems like the logical next step.
