Some random thoughts:

Are you looking for a tool that helps people create metadata in a consistent way - build schemas etc? Or are you looking for a store in which people can 'deposit' their metadata?

These are overlapping ideas, but I think they are distinct - for an important reason. I don't think you should build anything that *relies* on a central store. I'm not saying you shouldn't build a store, just don't assume that all relevant metadata will end up there - it won't - you won't be the only community of birdwatchers etc. so you have to embrace the idea that other communities will be building relevant metadata outside your store.

The idea of linking discovery tools intimately to your metadata store worries me - we've just realised this is a problem for libraries!

I'm not sure the distinction 'available on line' and 'not available online' are very meaningful when talking about metadata - if you are only talking about a tool that deals with metadata, and that metadata points to the location (whether online or not), then the function is exactly the same - what differences do you see?