He's the protagonist. He's seen in the leak with Cora and drak. He's seen in the trailer with them. The Protagonist shown during comic con in 2014 is the same model. I'm pretty sure there's nothing really more to debate about this topic. I suppose they only way we'll know for sure, considering everyone wants to make assumptions about it, is E3.
Yeah, I dont buy into this theory at all.
The trailer shows off what appears to be an exploration party scouting out and surveying an uncharted area and then charging at what appear to be for lack of a better word 'Transforming' buildings that emerge from under the flowing desert sands. (It honestly looks like Rannoch but thats not where I'm going with this.)
The trailer is symbolic. It shows off an explorer who's clearly searching for something which turns out to be dangerous, a search that ends abruptly. His face is covered so is the female (So there's no guarantee she's even human.) who (on a place looking like Rannoch.) appears to be wearing Ashleys armour from ME.
Which to me suggests a TL.
We know that it takes place in the future due to travel time on the ARK. Cora is a companion in the future. Wearing Ashley's armour would be as effective as attacking the collector base with an MG44.
So I think we're looking backwards at events that have already taken place and probably lead us toward a dramatic plot twist involving this guy or the legacy he's left behind.
He's a trailblazer, that's his team and you're walking in their footsteps.
Edit: He's just an old cowboy who went riding out one dark and windy day.....