The feature I want most from hackernews: I want to make sure I don't miss any frontpage post in a topic of my interest.

It could be a browser extension that shows a little star beside the title, or maybe a program on my machine that emails me a bunch of those links at the end of everyday. Either way, no ML or trying to predict what I want - I'm just going to give it some keywords.

Now matching a keyword to a post can benefit from some nlp, and that'd be fine. Something simple like tf-idf should probably be enough. As long as the recall is close 100%, low precision is okay.