I don't think the knight could be Simon at all, the guy who Jellal killed in tower of heaven, because it would pretty much contradict the previous storyline since Simon was a "puppet" when Erza, Jellal, and katana girl were fighting the Spirrigan 7 man with reanimation magic, bringing back the body and "soul" of Simon but controlling him even though Simon was able to think for himself in the puppeted state. The magic was also able to be used on people who were only dead and the only time we actually saw someone getting fully revived with magic was when Wendy revived Jellal in the early chapters of Fairy Tail. Simon also likes Erza so there's no reason for him to want to fight her to test her strength since he already knows she's strong and he knows how to use shadow magic so he wouldn't really need to use armor and a sword. Unless the knight is an Edolas or Elentear version of Simon, I doubt it could be him at all since he's fully dead on Earth.
I don't think the knight could be Simon at all, the guy who Jellal killed in tower of heaven, because it would pretty much contradict the previous storyline since Simon was a "puppet" when Erza, Jellal, and katana girl were fighting the Spirrigan 7 man with reanimation magic, bringing back the body and "soul" of Simon but controlling him even though Simon was able to think for himself in the puppeted state. The magic was also able to be used on people who were only dead and the only time we actually saw someone getting fully revived with magic was when Wendy revived Jellal in the early chapters of Fairy Tail. Simon also likes Erza so there's no reason for him to want to fight her to test her strength since he already knows she's strong and he knows how to use shadow magic so he wouldn't really need to use armor and a sword. Unless the knight is an Edolas or Elentear version of Simon, I doubt it could be him at all since he's fully dead on Earth.