I still want Apple to make a Hub thing inside iOS. I hate having to use 6 messaging apps to reach people I love, but as a 'data providers' I'd keep them installed.
Microsoft tried doing something like this with Windows Phone. It was OK, but the fundamental issue here is that the messaging apps themselves absolutely do not want such a thing, because it would commoditize them and keep the user away from revenue-boosting gimmicks and dark patterns. They will never allow it to be built. RIM was only able to do it before companies realized the value of messaging lock-in; even if it still existed in any real capacity today, this feature would not.