Hey, sure... I'll bite.

That doesn't look like Wu Kong, as hilariously ridiculous as that frame looks... what, with his NERF-bat double lightsabers. Appears to be Excalibur Umbra, the Chinese "exclusive".. by which I mean only for about a month, then we're getting him here.

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You'll notice the pose is roughly similar to that of the vine, that and his horn-less helmet. Chances are, "The Second Dream" is going to be what Update 18's chapter will be called, not to mention that we're on version 17.8 as it is. It's about time for that new chapter, give-or-take a few "Tenno Reinforcements".

EDIT: I take that back. He actually DOES have a horn.

Stalker upgrade? As awesome as that sounds, I doubt. The head (or at least what i think is its head) seems similar, and the frame definitely has Excalibur's features, but that's exactly the problem. If they decided to overhaul the Stalker, it's safe to assume they would overhaul his appearance as well, but it seems like minor changes at most from what we can see. Even if it's just a buff, i doubt they would be teasing us with that alone. Now... Perhaps complete Stalker backstory/questline? I think that's more feasible.

I feel like pointing out just couple things. Instead of typing a novel, i'll use my terrible editing skills to get a better picture.  

My "findings":

I think that Stalker, Excalibur or whoever it is, is down in a sort of kneeling pose (like the Tenno kneel) with a sword resting against his shoulder and/or neck.

Actually, that would make a lot of sense, considering in a recent devstream, there was a question about Stalker buffs, and they kinda deflected it, so someone decided to tease either the PBR'd Stalker, or.... maybe Stalker Prime? Stalker Umbra even?