Keep in mind that this also doesn’t necessarily mean that we won’t ever see Steve Trevor III or IV in the modern era; it will just be someone else playing him.
It’s worth noting that Chris Pine signed a multi-picture deal when he joined Wonder Woman, which is typical procedure nowadays with major actors on superhero movies.
That said, DC and Warner Bros made not decide bring him back for a Wonder Woman sequel or another DC Extended Universe entry.
Even if they do, unless the events of Wonder Woman somehow lead to Steve Trevor being put in some kind of stasis, his appearances would be limited to flashbacks or dream sequences/hallucinations.