Rather than posting my assorted thoughts on what this means or what's up next, I'll just say 1) yes, Deadpool can be nominated for Best Picture, and 2) I kinda hope it does.
My reasons for hoping that Deadpool gets nominated is...well...I like it more than Fences, Hacksaw Ridge, Hidden Figures, Loving, Lion, Nocturnal Animals and the list keeps going...so fuck it? Why not? Isn't this why they expanded their roster in the first place? To nominate popular movies that audiences and critics enjoyed? Deadpool is trendsetter (in its own way) like The Dark Knight. I'm 100% in favor of reducing the lineup to five, but until they do, fuck it.
Can it get nominated? Sure. I don't think it's likely, but Deadpool has one advantage. It stands out from the crowd. For the most part, there are three big films around which support has galvanized (La La Land, Manchester by the Sea, Moonlight) and Arrival has probably joined that crowd. Then there is a slew of films that tend to blend together in my mind at least as having roughly the same level of support and identity. The closest comparison would be Guardians of the Galaxy, but I would argue that Deadpool is in a much stronger position with precursors (nominations from the PGA, WGA, and Golden Globes), with the industry (it's a trendsetter and a star vehicle), and competition (the lower-tiered competition in 2014 were American Sniper, The Theory of Everything, Selma, and Whiplash). Right now I'm not betting on it getting in but could it happen? Sure.
“This is something, as long as we live in a world where something means anything. I’m not sure we do anymore. It seems serious, but do we live in a world devoid of consequences now? This seems like a seismic event, but it might be nothing.” John Oliver