Ideally I would like to access the ratings (thumbs up/thumbs down) on the criteria of a product/place across clients. So I'm trying to find a way to do that without centralising the control over the list of criteria.

With the current nip it's only the total score that has to be interoperable, so that's the real "need" in the end. My suggestion is more of a "wish", because current reviews suck 😉.