I took another long look at the picture of the surviving fragments from the neckline of the Pskov shift and now am inclined to agree with the reconstructors that the shift probably did open in the front, after all.
It's a bit easier to see in Peter Beatson's sketch of the neckline fragment. There is a short bit of pleated neckline, then the end strip/string, which is knotted to a end bit/string on the other side, which leads to a longer pleated bit in the back.
What has changed my mind is the short pleated bit. In the photo or sketch it shows up on the left-hand side, at the bottom, At that point, there is only a short bit of pleating (about a centimeter) before the rest of the fabric strip securing the pleats extends into a tie string. That tie string is shown knotted to another tie-string piece on the other side. Meanwhile, to the right of the small pleated bit is another piece, only loosely connected to the small pleated bit, which is a larger pleated bit, about 4-5 centimeters long.
It occurs to me that you could make the shift in one of two ways that may give such an effect. First, you could use three pieces of fabric; one extra-wide (i.e., much wider than the wearer's shoulders) for the back of the shift, and two other pieces, each half as wide, for the front. The front pieces would be seamed together up to the point where you wanted the slit to begin. Then you bind the slit (or perhaps just turn it over and give it a tiny hem), sew the shoulders together and pleat the sides and hem to neck size. If you used two separate strips to pleat the sides and become tie-strings, and a third strip to anchor the pleats in back, the result might have the segmented look of the Pskov fragment. Alternatively, the same approach might work if you took two extra wide pieces of fabric, sewed them together at the shoulders, cut a slit down the center front, and bind, pleat and anchor as above. The beauty of this approach is that no armpit gussets or gores are required; only the front/back pieces and two sleeves. This may be what the reconstructors had in mind, judging by how wide the shift is in their sketch.
The only questions are how wide you need to make the shift to make this all work, and how big the shoulder seams need to be. Or, to put it another way, how much of the fabric needs to be pleated into the neck. I suppose I'll take the widest sections of fabric that I can given the amount of linen that I bought and experiment.
Any other thoughts? I'd love to start a debate on this.
When I get the shift together, I'll post pictures, both before and after I get the red silk trim at collar and cuffs sewn on. EDIT: Ooops! I mean, I'll post pictures both before and after I get the red silk trim at hem and cuffs sewn on. The neck is gathered, of course, so no silk trim there!