You are using infinite scroll, it's great.

Which means, you load X element, then when we are close to the end of the loaded elements, you are preloading the next X elements, and so on.

But if you are using "n" key to navigate into a feed, you may face the following issue.

Let say that you want to read a feed that contains a lot of articles thats contain a lot of text or images

You may consider that few of them are interesting, then by reading the title you will know that you don't need to read the article.
Then you will use the "n" key to go to next article.

You will face an issue if the last item is a huge post, (I mean larger than your screensize) then you won't be able to use "n" key

You will have to scroll down (by using space key or elevator) until your system will detect that you need to load more elements.

According to me, you should consider to load the next elements when the last item is selected.

Here is an example of feed with huge content (lot of text and image)

http://fulltextrssfeed.com/feeds.feedburner.com/packfs