This is a (multiple allowed):

• bug
• enhancement
• feature-discussion (RFC)

SASS for having navigation buttons at the top and bottom
(and pointing up- and downwards) for a slider in vertical direction:

.swiper-container-vertical {
  .swiper-button-next,
  .swiper-button-prev {
    left: 50%;
    transform: rotate(90deg);
    transform-origin: left center;
  }

  .swiper-button-prev {
    top: 10px;
  }

  .swiper-button-next {
    top: auto;
    bottom: 10px;
  }
}

Hm, the transform rotation makes it a bit difficult to position. The arrows are slightly offset.