Hoi,
What I have read is that it will be individual items that are graded. That is not what helps you determine what items are lacking in something. When you want to determine if something is lacking you need a relational approach. When you approach a award like this one [1], it was added to make the award for a person [2] more complete. No real importance is given to this award, just a few more people were added because they are part of a group that gets more attention from me [3]. For yet another award [4], I added all the people who received the award because I was told by someone's expert opinion that they were all notable (in the Wikipedia sense of the word). I added several of these people in Wikidata. Arguably, the Wikidata the quality for the item for the award is great but it has no article associated to it in Wikipedia but that has nothing to do with the quality of the information it provides. It is easy and obvious to recognise in one level deeper that quality issues arise; the info for several people is meagre at best.You cannot deny their relevance though; removing them destroys the quality for the award.
The point is that in relations you can describe quality, in the grading that is proposed there is nothing really that is actionable.
When you add links to the mix, these same links have no bearing on the quality of the Wikidata item. Why would it? Links only become interesting when you compare the statements in Wikidata with the links to other articles in the same Wikipedia. This is not what this approach brings.
Really, how will the grades to items make a difference. How will it help us understand that "items relating to railroads are lacking"? It does not.
When you want to have indicators for quality; here is one.. an author (and its subclasses) should have a VIAF identifier. An artist with objects in the Getty Museum should have an ULAN number. The lack of such information is actionable. The number of interwiki links is not, the number of statements are not and even references are not that convincing.
Thanks,