Nicolas,
Your mail makes my Wikidatan heart beat with delight! Yes, this is definitely the direction we need to go, but sadly, not all Wikipedias will adjust their policies at the same rate.
I think we should start by getting this conversation off this mailing list and start to work on some project pages on Wikidata. Right now we only have these:
There is no "Wiki Loves Monuments" page yet but there should be a whole category, like what we have for SoaP here:
My original mail in this thread is about moving the monuments db which is currently here:
We need to split that up and move it to Wikidata in all its bits and bobs.
Jane