Yeah, I've actually thought about this for some time - in relation to all headphones and not just IEMs of course. And I'm kinda with Silent here. Actually, the solution I came up with involves a massive database that let's people customize what THEY want to see/compare. Of course, then we run into the problem of data gathering/entry, which would be a monumental task in and of itself. Ain't nobody got time for that!
Pretty much the only way to do any meaningful retrieval would indeed be an SQL database. Unfortunately as there are no standards for performance it is well nigh impossible to have meaningful data at all. I'm sure some would love to see a bunch of FRC's and CSD data plugged in so you could make decisions on that. Once again that data is largely meaningless as it is genereated in the context of the testers "pet" system. Also It would not tell anything about build quality, durability, style etc.
About the only thing you could do would be a Wiki type thing where you start out with the manu specs and let owners fill in other details as they emerge.