I am also very interested in using the RSS Feed Macro, but it is not available in the Macro Browser. I see that there are a lot of restrictions for On Demand: http://confluence.atlassian.com/display/AOD/Restricted+Functions+in+Atlassian+OnDemand
But the RSS Feed Macro is not explicitly restricted. It does say "user macros" are restricted, but I believe the RSS Feed Macro is not a User Macro.
I will try requesting the feature be turned on by submitting a ticket here: https://support.atlassian.com
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