The idea is not new - has been done for a lot of XPort's emulator ports on the XBox. I think the problem is: how do you filter "crap" entries? It would be cool if there was a central database for "working" DOSBox configs, but i don't think it would make sense to make this databse "open for all". The quality of the entries just wouldn't be good enough. And i think another issue would be database updates. On every new DOSBox version, every entry would have to be re-checked, to verify it against the new version. There's other issues, too (for example, how do you match a config with a specific game/game version?). The "database" on the DOSBox website is already quite good, but not very up-to-date.

I think the Rubybox database uses an EXE-checksum.

Edit:

RubyBox uses game name and checksum of the .exe to search for matches. For example if you add a game named ultima to list and press import, it should (currently) find two hits and ask which one to import. Same should happen if you add the same ultima 5 .exe, no matter what you name the game.