Did you read this thread, Stéphane? What if the Landrace Community had a way of swapping seed as effective as this Scion Exchange (based in France)?
I like your idea and it makes me think of that.
A more simple version would be a catalogue. Our local seed saver association does something like that. There’s still a database with all the info on the crop types. Then every half year you signal in the user database which ones you have seed of. Two administrators collect the catalogue and releases it.