I always answer these kinds of questions from my own experiences as a reader. For me as a writer it is irrelevant, how many other authors have done this or that; the deciding factor is how I feel about it as a reader.
So my first suggestion would be that you find examples of what you want to do, read them, and see how you feel about them. I can't really give you a lot of examples, one (Philip Pullman's His Dark Materials) was mentioned in a comment by @Filip, another one is Ally Condie's Matched trilogy.
I think that it is important that you come to your own conclusion regarding this, because readers are just as different as writers, and if you like reading trilogies where the second volume adds a second POV, then others will, too, and you should write it that way.
But I want to give you my own opinion, and try to explain it. Maybe it will give you some useful insights.
When I read, I very strongly identify with the main protagonist. For that reason, I generally don't like books with multiple POVs as much as books with a single POV, but I will read a multi-POV book, if it is really good. I have written elsewhere on this site, that when I read George R. R. Martin's Song of Ice and Fire, I used to read all the chapters of one character, and then all the chapter of another character, instead of in printed sequence. I did this, because when I came to the end of a chapter and was forced to switch to another POV, I was so engrossed in this character's experience that I simply couldn't care about the other character.
The same happened to me, when I read Ally Condie's Matched. To me, the first volume was a really great read. I enjoyed "being" the protagonist, and living her life. The reason I picked up the second volume was that I wanted to live that life a bit longer. But then the second volume had two POVs, that of the first book's protagnoist, and that of her love interest. This was a major disappointment for me, because I simply did not care about the other character at all. I cared about him as the love interest of "myself", of course, but wasn't really interested in "being" him.
So, while the book (as well as the third volume) turned out to be quite okay, I never got into them as much as into the first volume.
I'm sure there are other readers like me, who get into their protagonists so much that they hate being forced to switch POVs. Your book will fail these kinds of readers. But I have no idea what their percentage is, and how much other readers love to switch. Maybe there are those people, too.