Great idea. Reminds me of a previous HN comment [1]:

    How to build the next Google: all good results these days are within
    communities, and Google search has become useless for most of these
    searches.

    So don't build a search engine: build a "rotten tomatoes
    for X" where the sources for each X are "the top N
    subreddits/communities/editorial-sites/forums for X".

I’d be curious to know how you plan on covering costs.

[1]: https://news.ycombinator.com/item?id=24714546