Whatsapp is the defacto messaging app in my home country yet I have never seen anybody complaining about it not having SMS integration or using the pure SMS app for SMS.
Right. That's because most people have moved away from SMS, which is the trend in most worldwide countries.
In the US it seems SMS is so heavily used and that's why we have people clamoring for integration. But at the same time I challenge these people whether they understand if there's a need for integration, or if they think the word "integration" is cool and if they can have an "all in one product" for two+ things they use, it's cool.
I see very little need for integration, and if anything it's better to just get the US userbase onto Whatsapp or Hangouts rather than to have integration. To me, SMS has a certain type of urgency reserved for when you're trying to get ahold of someone like calling. Whatsapp/Hangouts conversations on the phone can be a mix of that as well as casual chat. Then there's also Hangouts conversations on your computer which are more for passing the time. It's been difficult to integrate the latter 2, and now Google's trying to mash SMS into that. Why not just integrate my email into Hangouts also for the sake of "integration." Maybe record my voice conversations too and put it all there.