The problem is, the feed/stream API endpoints for most of the services mentioned above, either do not exist or have been removed.
- FB and Instagram no longer provide them, for sure.
- WhatsApp doesn't have an official API - the last time I test-drove Yowsup, my number was 'blocked' by WhatsApp.
- No idea if there's an API for iMessage, although I get the feeling there mightn't be...
Screen-scraping all of these services is way too much effort for way little reward. Not to mention that FB keeps 'updating' its UI/UX quite frequently and Instagram doesn't show a 'feed' on the web if you login.
- FB messenger is based off the XMPP protocol, so yeah, there might be a way to access it without having to screen-scrape.
- There's a free/paid service called Integrated Inbox which integrates Google's services: http://integratedinbox.com/plans/
That leaves HN, reddit and the Google gang - is it really worth the time to integrate these into one service? Maybe one could build the basic structure over the weekend and then provide an option add-on different sites as a 'plugin'...