Smartphones are the only form of technology at that level of popularity. Everything else is much less popular, even TVs.

So I don't think 'the next big thing' has to be as popular as smartphones to be honest.

I expect AR will get to that stage, but with VR taking off before AR, I can also see it being 'the next big thing' on the same level as something like PCs.

The reason why is because unlike a console, VR has many more uses. It's effectively a general purpose computing platform.