It'll be about February 2017 that people will start hating the game.
S/M have a number of pure, factual reasons as to why they are disappointing; everything from some features not delivering, many ordinary features being absent for no good reason to big gaps in the games content.
Despite this, a lot of people like S/M because they find the story appealing and are enjoying the journey (Even if it wasn't fun for some of us).
In February though, not only will everyone have played it (There will be a big chunk of people who get it for Christmas) but Bank will have been available for a while and online will be full of people using Gen I-VI Pokemon and absolutely stomping the majority of Gen VII Pokemon into the ground.
At this point, everyone will go "Fuck this shit" and decide to catch previous-gen Pokemon to be able to play online, only to find that they can't catch the Pokemon they want - they have to transfer it with bank.
Some will be pissed off that they have to pay for Bank, others will just be mad that the majority of Pokemon can't be caught in Alola at all. At this stage they'll already be pissed off that they've seen and done everything in the region too and that's when people will start deciding that they need a sequel immediately because 'S/M is unfinished as fuck'.
