1/ I do not like the use of $CFG->forcehttpsforrss in rss/file.php - any session starting should be done by $SESSION global instance
we can not detect the https reliably in core now - major problems is the offloading of encryption to another server - my +1 to leave this out for now and fix the https handling in core first
2/ the rss should use contextid as module or plugin identifier now - we will be moving to this for all module/block files next week; the first implementation of new API should be finished in about 2 weeks from now
3/ rss_auth() does not respect the $CFG->guestloginbutton which also disables any guest login if disabled
4/ $CFG->forcelogin setting is not respected too I think
5/ calendar/lib.php - following if does not seem to be correct:
if (isset($CFG->enablerssfeeds) && isset($CFG->calendar_enablerssfeeds)...
6/ why the changes in require_user_key_login()?
7/ please watch your whitespace, especially the trailing spaces and indentation 
8/ do not initialise objects with NULL value
9/ use proper PHPdoc inline syntax to annotate all new functions/methods
10/ course_setup() must be used if you assign $COURSE global object directly
11/ I guess <br /> is not recommended if you want to separate the rss icons in footers, it might be hard to style with css
Today I was thinking about possible RSS feed upgrade path in 2.0, the current feeds are going to break anyway - we could start using a new file /rssfile.php and let the old one rss/file.php just display feeds with nice error messages including info how to subscribe to new feeds.
Is there any ETAG support planned? This could help with perf a bit, loading of user caps is not cheap.
petr
Development in progress...
Implement core functions ?
Secure existing RSS feeds in Moodle ?
Add option to force HTTPS for RSS feeds ?
RSS for Calendar(Upcoming events) ?
RSS for Recent Activity ?
MDL-12563fixed ?MDL-12563fixed ?