@simonwoods @cdevroe The Verge, WSJ are already well known. A blog search engine is to find/discover those lesser known blogs and posts, IMHO. So I agree with Simon. An RSS feed engine helps find fresh individual posts in near real time, but it helps if the user can dial back the results 1 day, 2days, 1 week etc. You have to be able to parse the content of individual feeds which is what gives an RSS search engine a huge advantage over a simple directory. A simple directory has a hard time categorizing blogs that have content about a wide range of subjects.
Other considerations: Human editing/curation – a human editor should have final say on a blog’s inclusion. This weeds out the made for Adsense blogs. Long term managment: bloggers move to new platforms and the URL of the feed may change in that move, therefore it is handy if a feed goes dead to have a crawler that will check the blog’s domain and try to detect a new feed URL. Otherwise you end up with a lot of dead wood in the index over time.
The other problem is getting people to use you blog search engine. That’s hard to do these days. Once you have a reasonable index of feeds I would suggest working with makers of feed readers to offer your search from within the reader.