A textual commentary on passages that differs between the Nestle-Aland Novum Testamentum Graece (28th ed.) and the Robinson-Pierpont The New Testament in the Original Greek: Byzantine Textform (2005) is in the making.
The editors are Jonathan Borland and Mike Arcieri. According to Borland, "the commentary intends to supplement Metzger's by offering alternative views of the manuscript evidence held by various major editors of or commentators on the GNT over the last three centuries."
Thus far passages in Matt 1-7 have been treated.
Update: Maurice Robinson have explained that he is not contributing to the commentary so I removed his name.