I've considered it a possibility since we saw him with the Gorosei, but an extremely unlikely one. I think it would suck. Shanks is presented as a carefree guy who cared about his friends/crew in chapter 1. Oden's flashback further fleshed him out by showing how close he was with Roger (who was the opposite of evil), and Buggy's flashback showed that he shared similar ideals to Roger.
So after this I'd find it ridiculous if he was truly evil and on the side of the government. I do find it suspicious that he is interested in maintaining the balance of the world and has kind of accepted the control the government has over it. I'd like to find out more about that. If you consider the prophecy from Oden's flashback and how Roger said they were "too early", maybe Shanks has been staying neutral until the prophecy is ready to be realized.
Oda claimed Shanks would be active this year so I assume we'll find out more.
I wouldn't write off anything at this point. Despite being the first pirate that was seen in OP, he's also the one we know the least about. While Oda has made him come across as a good guy for the most part, he's also made him an intentionally mysterious character. Oda might have made him come across as a good guy so there will be a greater shock when he's revealed to be evil, but I just can't see it.
I looked this up and it seems plausible, like many other One Piece theories. The abundance of mysteries about how various aspects of the story could go and the resultant theories are two of the best things One Piece has going for it that other series don't.
I can't see such a hypothetical reveal as being anything other than a contrived attempt at a plot twist. Right now, the only hint there could be anything nefarious about him is him being able to meet with the Gorosei, which seems more about maintaining balance and would come off as inconsistent if he was an ally with how scared the WG were over a potential Shanks-Kaido alliance. There's currently too many instances of characterisation from him going against the idea of him being secretly evil, with him at best having some more grey aspects.
Shanks was also introduced on chapter 1 as pretty chill, even giving Luffy his hat. It's pretty doubtful there will be a turnaround on this considering Shanks is tied to one of Luffy's goals in his pirate life. One Piece is just not the type of show to have things like this. We saw that in Marineford Shanks still wanted Luffy to return his hat in a dignified manner and in the Roger's flashback he seemed a pretty good kid with his sense of adventure. Oda even said the character that resembles him the most is Shanks.