All of the storylines in Loki also ties to who we think could become the Earth’s big bad.
With the Fantastic Four reportedly coming into play, as well as the X-Men mutants, we have plenty of options on how Kang’s meddling with time actually induces the creation of one of the next two villains, either:
A big bad who also has travelled through time (and based on this panel could completely wipe my theory of Kang by using him in his place), he could be one of the most compelling villains in history, if done correctly.
Anyways, yeah he’s had several incarnations that were magical in nature, as well as a genius at the level of Reed Richards. Kang’s (or Strange’s) messing with the Multiverse may very well bring Doom into play as the next villain on Earth. And with a nation called Latveria on his side, he will be one of the most complex villains to explore in this new age of the MCU.
The most well-known X-Man villain, he could very well be brought in by the messings of the multiverse, or all the energies being played with by Strange and Wanda may very well create the mutants. Or Wanda could go rampant like her comic counterpart did, and instead of:
She could very well say something along the lines of “No longer alone.” and bring more people like herself into the main continuity. i.e. the mutants. She’s already displayed a similar ability in WandaVision.
But yeah, Magneto could be a very compelling villain as well, in that he is a villain because he feels he has to be for all mutant-kind. And written well, that could be a story that could last through two phases with ease.