But then again, nothing is impossible. Making a new LEGO theme takes quite a while (Hidden Side, for example, isn't even a Big Bang theme, yet it they were working on it as early as 2017), so if it's Constraction, it's quite possible that they started working on it after Bionicle G2 ended, and planned it to release this year.
LEGO has been pretty tight on leaks lately, I doubt we will see anything until it's officially revealed (Most likely at the NY Toy Fair in February, like Hidden Side was last year) . Otherwise, we would probably have known what it is already.
18, to be more exact.