I agree. One thing I learned from the 2 previous TV shows is that they are not going to put anything too major that will make the movies confusing since Disney+ is not available everywhere. Sam became Captain America because in the movies Cap passed him the shield. There was never a possibility it could have gone different.
Same with Wanda, there was never a possibility of Mephisto because if he showed up in a movie and was like 'You know what I'm all about already because you watched WandaVision' then a lot of people would not understand the movie.
Therefore, I don't think Kang is going to be in the TV show since he's going to be a movie villian, but I do like this theory a lot. My money is on another Loki variant that created the TVA and they are going to take him down and allow for the timeline to be unstabilized, but it won't be all that important of a detail for the movies, they are just going to start unstabilizing the timeline somehow, probably via Kang.