The original rumor for the GTX 1070 Ti came from a listing of Asus' STRIX GTX 1070 Ti, so the newest tease from Gigabyte certainly adds some weight to it.
While it does not specifically confirm the GTX 1070 Ti, the teaser poster which was published on Gigabyte's official Facebook page says both carry the Ti mark and "coming soon" hashtag, as well as following the theme of the recently released It blockbuster movie based on Stephen King's book and the remake of the 1990 TV mini-series. Due to the horror theme, this could mean that the launch could have something to do with Halloween, which means that the launch could be scheduled for October 31st.
Earlier rumors suggested that the GTX 1070 Ti could be based on Nvidia's GP104 GPU with 2304 CUDA cores, putting it smack between the GTX 1070 and the GTX 1080. This makes sense as there is room to fit a card between the GTX 1070 and the GTX 1080 and should put a lot of pressure on AMD's RX Vega lineup.
Hopefully, we will hear more about it soon.