i think you could make this with tunisian. when it gets the the split, you could keep working half the stitches until both halves are long enough and then start stitching across the entire piece again at the other end.
Garment inspiration: An interesting, sleeveless cowl knit tube top one could wear with either end of the tube "up." It even has a halter-wear iteration. While labeled a DIY, it's just this series of s (Diy Ropa Patrones)