why use a query string? what about the good old file extensions:

http://cloud.example.com/apps/news/feeds.xml -> returns the requested data as xml
http://cloud.example.com/apps/news/feeds.json -> returns the requested data as json
http://cloud.example.com/apps/news/feeds.html -> returns the requested data as html
http://cloud.example.com/apps/news/feeds.atom -> returns the requested data in atom format
http://cloud.example.com/apps/news/feeds.rss -> returns the requested data in rss format

.....

some for requests to single resources
http://cloud.example.com/apps/news/feeds/245.xml -> returns the requested data as xml