At 23, Chan has pretty much reached his technical peak. He could clean up his 3a as best he can, but IMO it will never be a secure jump for him. At 27, he will be past his peak and struggling to retain his technical skills while being more injury prone. Fernandez is the same age as Chan but has a more impressive technical arsenal, with two different quads and a secure 3a; Javier hasn't quite peaked yet. Hanyu will be 23 and at his peak; he is working on more types of quads and should be even more formidable in 2018.
Chan is no Plushenko that he can still guarantee he can still peak at 27 or over
Chan's time was in 2014 but he lost to the talented wonderkid Yuzuru Hanyu
Yuzuru, Javier, Han Yan, Jason and many others will be ahead of him by then
he passed his peak and his over scoring peak. done. game over
Chan improving his technical arsenal at 27 would be pretty implausible. I think he can improve his consistency though. The problem at Sochi was that he showed he couldn't take advantage of Yuzuru "insane BV" Hanyu's mistakes even when Hanyu made them. Chan can still win if he learns to become the only consistent man in the field. ...That's probably a tall order though--maybe even as difficult as learning a new quad.
That being said, I don't hold too much stock in Hanyu learning new quads until he lands them in competition. There are many more people who landed quad loop/flip/lutz in practice than ones who actually did--or even tried--in competition (actually, nobody landed a ratified loop or flip). Hanyu's advantage is that IJS is so forgiving to falls he can try 'em and keep failing... and still win because of his BV.
Next OGM... well, both Chan and Hanyu will have their own difficulties. No Canadian man has ever won gold, and no man has won a second (individual) Olympic gold since Dick Button. So it'll be Canadian curse vs. reigning Olympic champ curse. Chan will be 27 and no one sans Plushenko has been a contender at that age; he did not go out dominating the field like Plushenko did either, but he hasn't suffered from the same degree of injuries. But Hanyu is a Japanese man competing on Korean soil, so maybe they'll screw him over.
More likely, someone new will emerge. Or Javier and Machida, being late-bloomers, could end up pulling ahead. All this isn't to say Chan shouldn't continue (I don't care either way); he'll still be near the top even if he isn't at the very top all the time anymore.
Machida seems to be peaking now, and he will be 28 in 2018. IMO, his presentation qualities rank below Hanyu and Fernandez.