The last, and least likely possibility, is that Ubisoft is teasing Far Cry 5 with these images, and the next mainline entry in the series actually takes place on the same island, featuring some of the same characters from Far Cry 3.
Translated from French, this post's caption reads, "An island that we never really left".
Since Ubisoft hasn't confirmed anything about this so far, the field is open to speculation. Maybe nothing. It could also mean Ubisoft is laying the groundwork for a Far Cry 3 reveal at this year's E3.
Revisiting the Far Cry 3 island is a bit of a risk for Ubisoft, given that the company was slammed for being unoriginal with Far Cry Primal.
We haven't seen a numbered Far Cry since Far Cry 4 in late 2014, with Far Cry Primal launching early past year. The first Far Cry game was remastered by Ubisoft Pune as Far Cry Classic for the Xbox 360 which was met with a mixed reception. Will we see Vaas again?
However, there are others who thinks that it might not be a port but a remake or a remaster since that seems to be what the game developers love to do right now. Or has your interest in the franchise diminished after multiple releases?
We don't know for sure.