As speculated Lego has revealed its secret revealing the below video (Linked)
"It is told that there exists a mask that will grant its bearer unspeakable power. Made from raw magic and solid gold, it is an artifact crafted with absolute precision and timeless skill – it is known as the Mask of Creation." - Bionicle 2015
The reveal is of the fabled 'Mask Of Creation' worn by Artahka and heavily implies that Bionicle 2015 is a continuation and not a reboot. In addition a new 'Bionicle' facebook page has appeared from Lego where you can talk about Bionicle. In addition the facebook page was made on the 10th July by Lego... so they've been planning this for a while.
After checking the Facebook's about section the 'mission' is described as
"Battle for the Masks of Power"
"We are ready to take you on an epic quest to find the Masks of Power. It will be a journey you will never forget"
As speculated the Mask Of Creation mould appears to use a similar system to the Inika with no inner stud pieces. Or for those familiar with Hero Factory similar to the helmet pieces. However it is also possible this is for the CGI version only.
Mask Of Creation Wiki; http://biosector01.com/wiki/index.php/Mask_of_Creation
Bionicle Facebook; https://www.facebook.com/LEGOBionicle
Lego Facebook; https://www.facebook.com/LEGO?hc_location=timeline
Twitter Announcement; https://twitter.com/LEGO_Group/status/512967202669342721
(Post is being updated to include more info/links)