But couldn't an app reverse engineer the frontends for all these communication services and create an aggregation overlay? E.g. what Dropbox did with the Mac osx filesystem.
Doing this within a mobile app is not practical for several reasons.
First off, the official mobile apps often use the platform's push notification service for asynchronous notifications of new messages. A third-party app can't pretend to be another app for push notification purposes (unless you jailbreak?).
Second, so if you can't access push notifications for async, then you need to poll or keep a websocket open. That'll nuke your battery life.
Third, the mobile platforms are quite hostile to this. There's been plenty of third-party YouTube clients that have been removed, and even more stupid things like controlling smart lights on your local network through their official, deliberately unauthenticated LAN API needs an approval from the manufacturer of said lights.
An app definitely can't reverse engineer the frontends for all these communication services. A skilled developer (or, more realistically, developers) probably can. They're not cheap though.
