maybe Superman had a epic battle with the new Gods over a dispute and resulted in the destruction of the DC multivurse. Realizing their mistake the new gods open a portal to a different reality sending Superman with the task of finding the creator of all reality. The new reality strips Superman of his powers and memories. Deep down Superman still holds on to his ideals and thus Steve Rogers is born.
@shannonI5 hmm, i suppose its possible, but answer me this. how does stevie hide all the powers superman has? Especially the invulnerability. I could see superman dimension hopping and assuming another identity there.