The main feature of Google Reader that we all used was the OTA syncing which provided an IMAP-style service for RSS, keeping track of read and unread articles and feeds to read. Once Reader is shut down then developers will need to implement their own type of service to remain somehow relevant.
And there are a lot of Google Reader apps out there, apps such as Reeder, Newsify and Mr. Reader which are all affected by the shutdown since they’ve been built around Reader. Some developers will no doubt be able to implement their own sync service but others may not.
Feedly have been working on a clone of the Google Reader API (codenamed Normandy) and have expressed interest at 3rd-party developers who already have apps that will be affected by the shutdown. What this might involve (and cost) hasn’t been announced yet but it’s a great lifeline for those developers who might struggle to implement their own syncing facility.
The catch? It runs on Google App Engine, another Google service. Whilst Feedly have the right idea, running it on another Google platform seems to be a bad idea in the long-run. What if Google decides to can App Engine? I understand why Google would want to shut down Reader since it can’t be monetized (sorry, usage is declining) but my choice of replacement will not be something that still involves using a Google service.
If a true replacement to Google Reader is to arrive then it needs to be totally separate from any of Google’s products and services.