So I've seen this news reacted to in a number of different ways on Tumblr. Mostly excited surpise for that he was even considered, or upset that he was cut. But I think there's one very important thing we need to see here.
Lego hasn't forgotten about Bionicle
This shows that they still clearly recognize how important the theme was and how much it ment to us, and are actually looking for ways to shown that. And personally I think that's amazing.
Would I have prefered Takanuva not been cut? Of corse. His inclusion in the movie would have been amazing, and I'm sure the writers would have found a way to make it work.
Am I upset that he was cut? No. I still love the movie we got, and this doesn't change that.
But what matters is that Lego still remembers, and they still care.