To clarify, the common sense problem is a hard one. It is similar to level 5 autonomy driving. That will take a while to solve. But what we are talking about here is kinda like Waymo cars which can drive themselves in ideal weather at slow speeds in Arizona. So in 2.5 years I think the best chatbots will be as far from having common sense as the current Waymo self driving cars are from level 5 autonomy. Which is to say they will be pretty good.
Ideal weather at slow speeds, with a professional human driver throwing road-condition curveballs at you and challenging your responses? I like my chances.
Keep in mind that you would have to differentiate bot's responses from those of an old truck driver, a snobby philosophy student, a conspiracy theorist, a stoner, a bimbo following latest Kardashians news, etc. Lots of different personalities of real humans who can throw curveballs at you during a chat session. I hope you don't expect to only chat with bay area devs? :)