Warning! Spoilers for Timeless #1 by Marvel Comics
In his observations of the main timeline, Kang the Conqueror has seen a threat coming to the Marvel Universe in the ultimate version of Thanos. In Timeless #1, Kang takes a look across the timeline and sees into different points in time, recognizing that something is distorting what he sees - which includes a new look at the Mjolnir-wielding Thanos, whose hammer is powered by the Infinity Stones.
The hammer-wielding Thanos hasn't made himself known in the Marvel Universe yet, but his presence has certainly been felt. In Thor, the God of Thunder was shown a vision of his future death, seeing the ultimate version of Thanos taking out the Avengers and controlling other heroes and villains like an undead zombie army. Thor revealed his nightmare about the Mjolnir-wielding Thanos and with his hammer going missing in action, it's possible the Mad Titan soon will acquire it and use it to wreak havoc on Earth's Mightiest Heroes. However, it's unclear when that version of Thanos will show up - but it's clear Marvel is planning something big for his arrival.
In Timeless #1 by Jed MacKay, Kev Walker, Greg Land, Jay Leisten, Mark Bagley, Andrew Hennessy, Marte Gracia, and VC's Ariana Maher, the future of the Marvel Universe is revealed. On one of Kang's observation stations, the Oracle Base, the supervillain asks to see what is happening to the timeline. The sequence serves as a look at what's to come in future Marvel Comics stories. Kang sees Doyle Dormammu striking his father with the Twilight Sword, a new group of Young Avengers on the rise, the Punisher working alongside the Hand, the moon being destroyed in the Great Reckoning, and lastly, Thanos wielding an Infinity Stone-powered Mjolnir.
As Kang notes, something is distorting his look into the timeline, as he reveals some of the things he sees shouldn't be happening and others are moving in much different directions than he steered or anticipated them to be. So, the look into the future of the Marvel timeline might not occur as Kang sees them in the sequence. Still, it seems destined the ultimate version of Thanos is coming.
Kang knowing about the ultimate version of Thanos coming to the main timeline is likely just a footnote in what he sees in the grand scheme of things. While the hammer-wielding Thanos could decimate the Avengers and kill Thor, it's likely Kang won't intervene as doing so wouldn't serve him much purpose. Although, if Kang the Conqueror feels its necessary, he could steer the timeline towards a different trajectory to change the future Thanos' arrival. Readers will have to wait and find out, as Timeless #1 is in comic book stores now.