I have used a three-needle bindoff to knit the gusset stitches together, picked up and added a row of mitered squares along the diagonal of the arm, and then picked up along the diagonals to knit the final rows of the last triangle to finish off the arm. As I want a taper to the lower arm, I will be knitting 3 rows knit, one row purl, and on every right side row make a slip2-knit one-psso at the underarm "seam". I will also make a double decrease on the knit wrong side row by moving yarn to the front, slip 2 sts purlwise through the back loops, purl one, slip 2 stitches over. This should provide a taper to the arm, and keep the bias knitting continuing as needed. As my arms conveniently are short, I won't be making small mitered squares here, but simply continue to end of the triangle. On the cuff edges, on every right side row, I knit1, SSK, knit to center underarm, S2K1PSSo, knit to last 3 sts, K2tog, slip1.
On wrong side rows, it is: K1, purl to last stitch, slip with yarn in front, alternating with a knit row which has the double decrease purlwise in the center, and slip the last stitch of the row with yarn in front. This will bind off on the diagonal at the cuff on right side rows only, and provide a slipped stitch edge at the cuff. I probably will do a garter edge for the final cuff, but I'll decide that later.. I'm enjoying how the striping is coming out on this, kind of asymmetrical but not too much. This colorway, 166, has some bright green and some pukey pinky greys, which I've used very sparingly. Luckily, this yarn is easily spit spliced, so I have been editing the colors! Lots of fun.