I think there will be one directory which will rival search engines in number of searches. It would need to solve the problem of having insufficient sites on top with a search algorithm. Below are factors I believe would be importaint in the ranking. This way the directory can be searched manually or by offered listings. Spam Domain Strength Age Popularity Satisfaction Relevance Scale And I think it will be a no follow directory
The directory would still need to crawl the web and index sites to build the moderation queue for the directory. Relying on humans to find every new site and assess it's quality isn't reasonable or feasible. The only advantage might be if it includes a rating system.
yes a rating system is necessary rate websites 1 - 10,000 and rank them in categories they belong in. There will rarely be ties.
The best chance of having one of these was DMOZ...and they're long gone. I don't see any web directories taking over search engines anytime soon.
I'm getting outranked by directories like Capterra frequently. What they do is buy Google ads. In this way first you have Google ads, and then you have directories that bought the Google Ads. In many queries it can be 80% ads on page 1 of Google (Adwords plus directories).