That we don't know. Perhaps they'll give him old man makeup like Soong in Brothers, and the poster would suggest he is the same Soong, but that one died in the episode. He'll play Soong's long lost half-brother
Why do I get the feeling that Noonien Soong has been retconned to, well, not be quite as ancient as he appeared (in "Brothers") before he died? There is a later TNG ep in which, IIRC, we see a hologram Soong recorded sometime before his death (about Juliana Tainer), and he doesn't look anywhere near as shriveled as in "Brothers". Perhaps Noonien died from some kind of rapid aging disease? I mean, in "Brothers", Soong knows he's dying and has presumably had time to prepare. So it would seem that some time after he recorded that holographic message about Juliana, Soong began to rapidly age out of control and died as a result. I guess that when the character of Noonien Soong was first created - long before he actually appeared - they really had no idea how old he was going to be, if and when he DID appear. I mean, remember "The Schizoid Man"? Ira Graves said he taught Soong everything he knows, yet appears much younger than Soong eventually would...
He's not Lore and he's not B-4. He's Data 2.0. The second version of a character we've seen before. Calling it now. After the ban on AI was lifted, someone in the Federation started working on creating a new Data and used whatever could be retrieved from the old Data: records, backups, interactions/activities, you name it. They're already trying to do something like that IRL where they think they'll be able to create a digital facsimile of a person one day. The only difference with Data 2.0 is that they'll be able to put the digital facsimile into a new body. It'll be one way to have Picard and Data have something in common. The only difference being: Picard is syntho-organic while Data 2.0 will be just synthetic.
What Spiner's character said initial teaser “Evolution is not an act of preservation, it’s addition!” Terry going on about how they want to keep him a secret, I bet we won't even see him in next week's trailer.
My wild speculation is that they're going to Genesis Planet Data and bring him back somehow. Sure it would undercut his death in PIC season 1, but look at what happened with Spock with ST II and ST III. Plus, he can also die a second time (again, much like Spock). Alternatively, they can always bring back Lore or B4 (they can use that magic doohickey from Season 1 to repair him.) Spiner can also play Yet Another Soong-type Android (TM) or Yet Another Soong Family Member (R). He can even be Noonien Soong in a fresh new golem body.
I said that's what I think they'd do. I didn't say what I thought of it. I expect Season 3 to have the polar opposite mentality of Season 1. That's the way it looks like it's being presented. Maybe, maybe not, but Picard did have Picard dying, and everyone having an emotional reaction to it, only to have him be revived in a new body. So it's not out-of-line with what's been done on this series. Before someone asks, "How can you say you think Season 1 and Season 3 will be polar opposites and still cite examples of what the series has done before?" The series is a coin. S1 and S3 are different sides of it, but it's still the same coin. If it turns out I'm wrong, no problem, I'm wrong, but that's my interpretation currently.
Brent Spiner to play a brand new character not connected to the Soong dynasty at all. He just happens to look like Data and Data related people. I mean, they did it with Talinn so why not?