Chuck Shotton gets to the heart of why Google Reader shutting down will be painful:
Here is the incredibly powerful thing that Google Reader provides that will leave a huge, gaping hole in my daily RSS reading:
Synchronization.
Google Reader was at best an average RSS reader. But it excelled at keeping all of my other 3rd party RSS reader apps in sync. By providing a set of APIs that allowed remote readers to mark/unmark individual articles as read, it let me start reading news on my phone with Feeddler, continue on my desktop with Google Reader, and switch to Flipboard on my tablet later in the day without having to wade through the same news articles twice. What was marked as read on my phone never showed up as unread on my tablet. It also gave me centralized management of all my RSS feeds. When I nuked an entire feed on my desktop computer, it disappeared from my mobile devices.
I wouldn’t hold my breath Chuck on someone filling the void. Matching the scale, speed, availability, and cross-client API support of GReader will be tough. Then again scalable data processing techniques and infrastructure have advanced far faster than the RSS reading population has. So maybe a small team can take this on as a side project, or even lifestyle business hustle.