Here are the main things that make me wonder if there is a connection between G1 and G2.
1. The Mask of Creation
As many G1 fans know, this was the name of Artakha's Legendary Kanohi. It was never revealed how it looked, though it was given a description.
"The mask was the most ornate anyone had ever seen – more than just a Kanohi, it was a true work of art. The metallic protodermis from which it was forged was arranged in intricate patterns and designs, each reflecting one of the many cultures that flourished in the universe. The eye slits were angular and pointed, giving him an air of both wisdom and a vague sense of menace."
This is a very similar description to Ekimu's own Mask of Creation.
2. The Vahi Easter Eggs in the 2015 Animations
Hidden throughout all of the 2015 Animations is a small reference to the Vahi, which was a Legendary Kanohi in G1.
The Legend - Cloud above Ekimu and Makuta shaking hands
Episode 01: Prophecy of Heroes - Ekimu's Crater
Episode 02: The Arrival - Tahu's Crater
Episode 03: Quest for the Golden Mask - On Okoto's greatest volcano
Episode 04: The Protectors Fight Back - Lava around Tahu's Mask
Episode 05: The Power of the Golden Masks - Behind Kopaka's Energy-Shield
Episode 06: Quest for the Mask Maker - Rock in Onua's Tunnel
Episode 07: Team of Heroes - Behind the hill of the Temple of Creation
Episode 08: Lord of Skull Spiders - Cloud behind Tahu yelling, "Onua!"
Episode 09: The City of the Mask Makers - Ruins of the Ancient City
If it had been in just one episode, I could understand that this was just an Easter Egg. But all NINE of them?
3. 'Unity. Duty. Destiny.'
While many G2 fans recognize this as the name for Episode 16 of the 2015 Animations, fans of G1 will also notice that these are the three virtues of Mata Nui.
4. The Nuva Symbols
In the 2016 Winter Wave, many G1 fans will notice that on the chest plates and the masks of the Uniters there is a Nuva Symbol, which in G1 was the source of the Toa Nuva's power.
5. The G2 Mask of Time
In the second BIONICLE graphic novel, The Battle of the Mask Makers, Ekimu the Mask Maker travels to the Temple of Time to use the finally-revealed Mask of Time. Before putting it on, Ekimu states the Mask is only half of a mask.
The G2 Mask of Time was cool enough on its own, but the fact that Ekimu said that it was the upper-half of the Mask of Time and hinted at it being called the Vahi is too coincidental.
6. 2016 Designer Video with G1 Reference
In short, a BIONICLE 2016 Designer (will get specifics later) said something like Umarak the Hunter's Hunter Mask was the G2 Mask of Shadows.
7. The Star Trek Comment
I'm pretty sure it was a member of the LEGO Group who hinted G1 and G2 could connect similar to the way the modern STAR TREK movies connect to the older Star Trek movies.
8. The Black Makuta with a Black 2015 Tahu Mask in the Makuta Contest Video
As fans of G1 know, when the Toa Mata first encountered Makuta, they found him in the form of a Matoran. The little figure has serious similarities.
9. Placeholders (?)
In the first BIONICLE graphic novel, the Mask of Time (which suspiciously looks like the Vahi of G1) is revealed to be the key to the summoning of the Toa. Many can argue that it is a place holder, but if it is, why have an UPPER-HALF revealed rather than a new mask entirely to replace the placeholder?
And of course, the thing which started this topic... The island of Mata Nui on the Mask of Control in the 2016 poster.
While we now know that Mata Nui doesn't appear on the official poster, why show it in the first place? Why didn't they have Okoto on it, as Okoto was already laid out in 2015?
These things make me suspect that LEGO is trying to get fans to look at/review the story of G1, so that the fans can prepare for the ultimate reveal... BIONICLE G1 is connected to BIONICLE G2!
Note: At this point though, I can't decide if I want G1 and G2 to connect or not.