I think it will depend on how they will tackle the franchise after the "Origin Trilogy" ends, meaning if they intend to release the next game in the next 3 years or if they want to take a bit more time to better figure stuff out, if they don't have those next steps planned already.
If the game is released in 2 to 3 years, I think we'll get new comics rather soon. Early 2019 I think.
If they end up taking more time to develop the game, who knows. I think maybe six months after they announce the game, to keep interest in the franchise up, and better set what Lara has been up too. Or maybe they make a graphic novel similar to "Tomb Raider: The Beginning" and release it near that game's launch. Or maybe they'll still begin a comic run in early 2019 and keep it more or less steady up until the release of the next game. All strategies are valid, so who knows?
But I do wish they keep making these comics, as I am quite enjoying
most of them