Well Brad Sam's podcast was leaking their E3, and focused on Scorpio, so yeah he's implying it'll be announced at E3, no?
Then after all of the Scorpio stuff leaked, Phil Spencer is on twitter saying lots of creative chatter today, can't wait to share our story at E3. I think it's clear he's responding to the Scorpio rumours, in that case, if they aren't revealing it at E3 what story do they have to share at E3 (taking the context of the tweet into consideration, unless I'm misunderstanding the tweet?)?
There's also the investigation Ekim did and found out two hardware consoles FCC NDA's expiring this year.
Couldn't it not being finalized be referring to upclock/downclocking, which can be done whenever really.
In response to your edit, if it's not coming out this year, I agree, they should wait until 2017 to reveal it at their event. But if it's going to be at this years E3 (or at any 2016 event), it's coming out this year IMO.