Think of the "reboot" (as it will inevitably be) in terms of an alternate universe (despite LEGO probably not ever admitting it's like that or doing a "crossover."). Look at Marvel and DC comics. They all have a main universe for most of their stories, but then they've branched out to other universes with the same/similar characters but with a few different traits in their characterization/portrayal/origin.
For example, many Marvel stories take place on "Earth 616." This is essentially our own universe but with superheroes. Every now and then we see someone hop over to another universe, with changes like other people being alive/dead that are dead/alive on Earth 616 or the social status/business position or someone (like a bad guy) being different. In 2000 Marvel started a comic book line called with the Ultimate universe, the Earth 1610 version of Marvel heroes. Things were different, but similar. Fans could enjoy the different stories now able to be told without worrying about continuity or repeating the exact stories (though sometimes the original story is retold with a twist somewhere).
DC Comics currently has Earth Prime and Earth 2, and every now and then we see Earth 3, or Earth 23, etc. Earth Prime is our Earth but with heroes and stuff, and Earth 2 currently has experienced a slightly different timeline. While there are many heroes that are recognized, they are vastly different from the Earth Prime heroes we know. They are getting entirely new stories without risk of rehashing things. Similar elements still might appear though, just with little tweaks.
So, I expect the same kind of treatment from Bionicle. We're going to see many similar things that remind us that yes, this is the Bionicle world we feel comfortable in. But we're also going to see many new things, from character armor* to bad guys and goals. Some of that is obvious with the whole "Mask of Creation" thing, some of it just might be wishful thinking in the hopes for change, familiarity, and some changes that are rooted in the familiar. Takua might not be the Herald of the Mask of Light, for example, but we might see the Avohkii pop up eventually. See what I'm getting at?
While a continuation of the story would be a great way to take what we know and grow with it through new stories, seeing a reboot will still take the familiar and still make new stories. And it makes it accessible to new fans ready to take in the new mythology.
*Armor/looks isn't that big a deal. Superheroes change their outfit looks all the time. Even the Toa Nuva did it in 2008.