Square Prepping A Final Fantasy Thing

What does this image mean? What is Square going to announce on January 17? Is this another mobile port? Is this something bigger? At least we only have to wait two days for answers.

Square recently put up a site with a teaser image for some Final Fantasy announcement that will be happening on January 17.

According to Destructoid, the enemy sprites are from Final Fantasy IV while the heroes come from Final Fantasy V and VI. What could it all mean?