It’s unlikely that Bionicle’s going to pull through. Compiling all the Space and Castle subthemes into one each puts them both ahead of Bionicle, and although Castle doesn’t appear to have made it, it Pirates will still get a bump from other System fans too.
In a way, yeah, okay, sure. Bionicle is a unique thing and not representative of Lego as a whole, even if it’s a very important part of Lego’s history. If Lego were handling this properly and having a whole line of Anniversary sets, like they did for Star Wars, then I’d expect Bionicle to be one of them. But if they’re only doing one, then yeah, it should probably be something more representative of the entire franchise.
That said, it’s very disappointing that the alternatives are Pirates, which has gotten some great sets in the past few years, and Classic Space, which has been Lego’s go-to Nostalgia Button for like a decade now.
EDIT: Switched to a version of the image without swearing