The legacy of Hans Küng's Doctrine of Justification lives on! The World Communion of Reformed Churches (WCRC) is the largest body of Reformed Churches in the world, and they have signed the Joint Declaration on the Doctrine of Justification on July 5th, 2017 in special ceremony in Wittenburg, Germany. The signing was witnessed by the World Methodist Council (WMC) who had signed the JDDJ in 2006, and Lutheran World Federation (LWF) and the Roman Catholic Church (represented by the Pontifical Council for Promoting Christian Unity) whom first signed the JDDJ in 1999, and was additionally witnessed by "representatives of the World Council of Churches, the Ecumenical Patriarchate, the Mennonite World Conference and the Pentecostal movement."  It's rumored that the Anglican Communion will also sign the JDDJ later this year.  The liturgy to the service was produced in six languages, and consisted of each attending party making ecumenical statements witnessing the signing, reciting the Apostles' Creed, and singing songs of unity such as We Are One In The Spirit.
The WCRC published a document titled the Association of the World Communion of Reformed Churches with the Joint Declaration on the Doctrine of Justification (Association) that explains the particular emphases and additional insights from the Reformed tradition that they wished to add to the JDDJ. Here are a few quotations from the Association document:
On the relationship between justification and good works:
We value the careful nuancing of the place of good works among the justified. They are the fruit (and not the root) of justification. Good works reflect the effect of God’s grace in us; faith that is active in love. Good works can only be done in dependence upon God’s grace. The Reformed would add here a comment on how we have interpreted the place of good works among the justified. In the Second Helvetic Confession (Chapter XVI, paragraph 6) there is an explication which clarifies that good works are not done in order to earn eternal life, or for ostentation, or for gain. Rather they are “for the glory of God, to adorn our calling, to show gratitude to God, and for the profit of the neighbour.” In this way, we have further elaborated the place of good works among the justified. (§37-39) 
WCRC adds that agreement on the Justification necessitates a renewed emphasis on social ethics, and opposing violence and injustice in the world:
For the Reformed, justice is not simply the ethical outworking of justification as a kind of second step; rather it is already entailed theologically in justification as such. This insight has now been elaborated in . . . “That both of these meanings are conveyed with the same word reflects the fact that they are profoundly related. The one who is justified by faith is called to act in a righteous way. As a consequence, the doctrine of justification cannot be seen in the abstract, divorced from the reality of injustice, oppression and violence in today’s world” (paragraph 56). Justification is, both a “declaring righteous” and a “setting right.” This insight may be at the root of John Calvin’s insistence that justification and sanctification are inseparable (Institutes, III.2.1); they are to be thought of as a two-fold grace (duplex gratia). We acknowledge that the declaration of justification (in JDDJ 4.2) as entailing both “forgiveness of sins” and “renewal of life” points in this direction. We also welcome the invitation offered in paragraph 43 to further clarification of “the relation between justification and social ethics.” 
The Association document says that Calvin, Melanchthon, and their Catholic opponents had almost reached a similar agreement to the JDDJ in the Regensburg Agreement of 1541.
There is a long and interesting history of dialogue on the matter of justification among Reformed, Lutheran and Catholic communions. In fact, a remarkable consensus on basic elements of the doctrine of justification was declared in the Regensburg Agreement of 1541 (Article V de iustificatione). Calvin warmly welcomed this agreement (Letter to Farel 11.5.1541). However, because of the confessional struggle, the efforts failed and the agreement was nearly forgotten for more than 450 years. 
I tracked down the cited letter from John Calvin to Farel on May 11th, 1541, and here's the relevant section of it:
Our friends in the commission have come to agreement on the doctrine of original sin without any difficulty; a discussion followed on that of free-will, which was drawn together out of the writings of Augustine; they departed in neither of these points from ourselves. The debate in controversy was more keen upon the doctrine of justification. At length a formula was drawn up, which, on receiving certain corrections, was accepted on both sides. You will be astonished, I am sure, that our opponents have yielded so much, when you read the extracted copy, as it stood when the last correction was made upon it, which you will find in the enclosed letter. Our friends have thus retained also the substance of the true doctrine, and, in that respect, you shall find me in complete agreement with yourself. However, if you consider with what kind of men we have to agree upon this doctrine, you will acknowledge that much has been accomplished. 
For more information on the World Communion of Reformed Churches (WCRC) signing the Joint Declaration on the Doctrine of Justification (JDDC), visit the WCRC's JDDJ website. And read my previous articles on the Joint Declaration on the Doctrine of Justification, and related posts.
In conclusion, I believe that the WCRC's signing of the JDDJ calls for celebration. At last, the Reformed tradition has joined in the ecumenical progress made by in the Joint Declaration on the Doctrine of Justification that was first started by Lutherans and Catholics, and then by Methodists. It is the 500th anniversary of the Reformation, and what better way to celebrate that anniversary is by coming together (rather than splitting further apart), as we may have hope in the future that many more churches would be united. The JDDJ is not the solution to all of our problems, but it begins the process of reconciliation, and allows more complete solutions to be discussed in the future.
[^1] "Witness to the Unity of the Church." (2017): 12. World Communion of Reformed Churches. World Communion of Reformed Churches, 5 July 2017. Web. 12 July 2017. <http://wcrc.ch/wp-content/uploads/2017/07/GC2017-WittenbergService-web.pdf>.
[^2] Heneghan, Tom. "Reformed Churches Endorse Catholic-Lutheran Accord on Key Reformation Dispute." Religion News Service. Religion News Service, 07 July 2017. Web. 12 July 2017. <http://religionnews.com/2017/07/06/reformed-churches-endorse-catholic-lutheran-accord-on-key-reformation-dispute/>.
[^3] "Association of the World Communion of Reformed Churches with the Joint Declaration on the Doctrine of Justification" (2017): 5. World Communion of Reformed Churches. World Communion of Reformed Churches, 5 July 2017. Web. 12 July 2017. <http://wcrc.ch/wp-content/uploads/2017/07/WCRC-Association-to-JDDJ-Total.pdf>.
[^4] Ibid. 6.
[^5] Ibid. 2
[^6] Calvin, John. Letters of John Calvin. Ed. Jules Bonnet. Vol. 1. Philadelphia: Presbyterian Board of Publication, 1858. 260. Print. <https://calvin.edu/centers-institutes/meeter-center/files/john-calvins-works-in-english/Letters%20Vol.%201.pdf>
Related: Hans Küng, Joint Declaration, Joint Declaration on the Doctrine of Justification, Lutheran World Federation, LWF, PCPCU, Pontifical Council for Promoting Christian Unity, Roman Catholic Church, WCRC, WMC, World Communion of Reformed Churches, World Methodist Council