III. Pauline Letters
IV. Catholic Letters
Now, the recently completed Catholic Epistles, although initially published in eight separate fascicles, is basically containable in a single physical volume (649 pages in my calculation); but the rest of them are not going to be. You would have to think that the Gospels, although ostensibly a single "volume", will no doubt require at least two physical volumes each (perhaps Mark may be able to be presented in a single volume); and probably something similar could be said for Acts (i.e. at least two physical volumes); while Paul’s letters will certainly also need to be published in up to six volumes, with Revelation requiring perhaps two. This would mean the total might be nineteen physical volumes - NINETEEN. And I am not counting the additional volumes of supplementary studies and textual commentary which are also promised.
By way of comparison, the Catholic Epistles take up 43 pages in NA27 (out of 680 pages in total); if this was representative and proportional we might expect the whole NT to take up 680/43 or 16 volumes. But the Catholic Epistles were chosen (I seem to remember this) partly because there are fewer manuscripts and fewer harmonistic type variants so the whole show is simpler in the Catholic Epistles. There are almost four times as many manuscripts of John than of the Catholic Epistles! So perhaps nineteen is an underestimation.
Anyway, I'm going for nineteen: you heard it here first, the ECM will take up NINETEEN physical volumes. Or do you have a better estimation?