This is such perfect design - succinct but also functional. I like the integrated ladder - looks not only like a part of the overall piece not an accessory, but also lot more functional than most bunk bed ladders. The original design is a little institutional but with some different color choices, pop a cork board behind the desk, could see this being a very happy place. I think an Ikea product for the desk area might make this go from drab to fab - not usually their biggest fan.
Also, for me, I’d lose the chair and just put the desk lower so you can sit on a cushion on the floor. More comfy, less cramped.