You know, in general, it actually kind of makes sense.
He's already got Pudding.
He tried to get Hancock. I don't know if he'll try again or not. But, he is interested in her.
And as for Hiyori, there is actually a reason he would go after her, specifically. She's a musician. And music, for whatever reason, does seem to be somehow important to getting the One Piece. A lot like Luffy wanting Brook, I think Blackbeard would want to get a musician for his crew. And Hiyori would work. Or maybe he could just use her as a human shield to escape Wano after trying to steal Pluton. Both work.
And, I'm going to add another possible kidnapping victim to the list. I think Blackbeard might end up trying to steal Vivi from Big News Morgans. Why? Because Imu wants Vivi, because she's so similar to Lili. Blackbeard wants to gain nation-status for Hachinosu (probably as one step in a larger plan). Therefore, it just makes sense for Blackbeard to use Vivi as a bargaining chip to get closer to Imu and get what he wants.
And Blackbeard did seem to know that Saturn would be on Egghead and sent his men there to get a "copy" of him. Blackbeard might already know that Imu wants Vivi, because Blackbeard might be connected to the "Gorosei psychic network" that they use to communicate with each other. Blackbeard might have a way to listen in to their conversations, possibly just as a natural ability of his Darkness Devil Fruit. Plus, Vivi needs to meet Imu, if only for the audience to find out more about Imu's backstory.
Plus, there's some theories floating around the Big News Morgans might have some connection to Blackbeard, anyway. Some people have pointed out that Morgans tends to de-emphasize Blackbeard in the news, when he can. He focuses on other people more and makes them the center of the stories, instead of making Blackbeard the story. It's possible that Morgans and Blackbeard could have some sort of connection. We'll have to see. So, maybe Morgans is bringing Vivi straight to Blackbeard, anyway?
So, yeah, I could see Blackbeard kidnapping a small army of women for the endgame. Just so that Luffy has a BUNCH of women he needs to save this time around, instead of just one like normal.