For a start, it is by definition thoroughly covenantal and takes into account the single purpose of God to deal with sin, sinners and the sin damaged cosmos through Abraham's seed. Second, this single plan of God gives one a sense of the meta-narrative of Scripture marching towards God's glorious conclusion. The sovereign plan of God in Christ is the focus of all narrative. (Why don't us Reformed guys like this?) Thirdly, given that God's covenant is about righting wrongs, i.e. judging sin, justifying sinners, defeating evil, restoring the cosmos, "the righteousness of God", when defined as "covenant faithfulness" is still thoroughly forensic as it denotes a thoroughly forensic covenant. It can and should protect the doctrine of justification sola fide. Fourth, the sheer scope of the definition of the covenant answers a lot of the evangelical/western individualism that the Reformed community are rightly anxious to counteract. If the covenant is about dealing with sin, sinners and the cosmos, then surely all the "me and my personal experience of Jesus" stuff gets drowned in the utter magnitude of this covenantal tidal wave?
Through this definition, the imputation of Christ's righteousness need not be abandoned but can be understood even more clearly. If God's covenant faithfulness accomplishes the righting of wrongs through the faithfulness of the last Adam/Israel, then this highlights even further that Christ accomplished by his works what Adam and Israel failed to do.
Maybe NTW, Dunn and Kaesemann have given us a tight exegetical answer to the question posed by "the righteousness of God". Maybe they haven't, I'm not too sure.
Now if NTW could just sort out his understanding of justification. Schreiner is absolutely correct to state that he didn't manage to answer the question Piper posed in his book, i.e. how does Wright's view of final justification according to works, while being justified by faith in the present actually fit? How does it work? I've read a large chunk of Wright's book, and I still see no answers. Maybe he doesn't know himself?! Whatever way it works, it sure doesn't sound like (the) good news.