Responding in my capacity as "money manager" for Dokuga, I have to say that this site could not host something of that magnitude.
It would be far too large and managing it would be, essentially, a full-time job - and not just for one person either.
For example, Dokuga hosts almost 10,000 stories, between the A-Single-Spark archive and our own. Our site size requires a dedicated server, and costs around $234.00 per month
just for the hosting. What you're envisioning is a site that, in essence, contains snippets of each chapter of every story - given the 10,000 stories here and the untold number of unique stories posted elsewhere, that's a monumental undertaking which would require a unique site of similar size.
You would need to take into account the fact that different sites have different ratings restrictions, and would either have to find a way to ATTEMPT to restrict access to adult material, or make such a site membership-only, similar to some Yahoo!Groups. Otherwise, you run the risk of being embroiled in legal battles over providing minors access to such materials.
In addition, in order to make such a site work the way you envision, you would have to have a search engine that is far more complicated and complex than even those that exist on the largest fanfiction sites. Obviously, that would probably require a certain level of programming expertise.
It's a terrific idea, but I think that, given our members' expertise and memory banks (lol) we do just as well with the "Searching" thread on the forum. Very few stories go unfound, even if some of them have long since been removed from the internet.
~~Wiccan~~