I really needed an RSS feed for my Discourse instance because it is not so active but when someone is posting I wanna know and I often forget to check it.
Then I remembered I already used Yahoo! Pipes to create RSS feeds for other sites not providing them, so I quickly created this:
You can test it while making it and see the results in the bottom of the screen. Once finished, save, then run pipe, then choose “Get as RSS” and copy the URL that opens.
The XPath query string is: //div[contains(concat(' ', @class, ' '), ' topic-list ')]//a[contains(@href,'/t/')]
Results can be seen here: http://pipes.yahoo.com/pipes/pipe.run?_id=f3dfeafb497bb8bad79a3d2dca745ba5&_render=rss
The only problems I see so far are a) it shows only topics displayed on page load and 2) pinned topics are pinned in RSS feed too 
Then this was a waste of time - this topic can be closed.