My issue with that is, it would make the writing absolutely terrible. Like, making the guy interested in smithing/forging *wink wink*, giving him a murky past and connections with a people who allied with Morgoth *wink wink*. Maybe I've just been spoiled with Better Call Saul, but I swear I will facepalm in real life if Halbrand really is Sauron. I refuse to believe it's him, and am assuming Sauron isn't in the show yet.
Let's say it is Sauron. Why would he have been on that boat?
Edit: I think Halbrand will become one of the Nazgul.