Moral Concepts as Unsystematic on the Introduction Side

Here is a metaethical idea which I find appealing and under-explored. What if what makes metaethics and the cognitivism vs. non-cognitivism debate so difficult is that we have failed to consider a certain possibility. Namely, that expressions can count as expressing concepts if there is enough systematicity in what happens once an application is accepted, even if there is much less systematicity in what happens before an application is accepted. 

On the view I am interested in, the reason moral terms count as expressing concepts at all, and count as linguistically meaningful, is that they are fairly systematic with respect to what lies downstream from them. This is compatible with them being much less systematic with respect to what they lie downstream from - and it looks like they are much less systematic in this respect.

By analogy to natural deduction systems in logic, we might think of moral concepts as coming with elimination rules, but no definite, agreed-upon set of introduction rules. 

So, concepts like right and wrong have fairly systematic and shared relationships to, roughly, what follows from statements involving them - in terms of other statements following logically, but also more probabilistic effects, and motivations and actions flowing from their acceptance. This systematicity is what makes them concepts - and it is enough! When it comes to what licences their introduction in the first place, on the other hand, there just isn't much there in the way of tight, systematic connections. Or there may be quite a bit there, but still not enough to, for example, motivate the view that these concepts are co-extensive with any of what we'd happily call descriptive concepts. 

On this view, the famous Open Question Argument comes as no surprise. Maybe you can always, under any descriptive supposition, intelligibly still ask 'But is it right?' - and that is just because there simply are no tight systematic links of the right sort between uncontroversially descriptive concepts and moral concepts. 

(By the way, the view isn't that all such concepts - concepts with unsystematic introduction behaviour - are moral concepts. The moral concepts are a subset of these, and what distinguishes them as moral as opposed to, say, aesthetic, has to do with what lies downstream from them.)

I wonder if this sort of view has been anticipated, as it strikes me as having real potential.