Came across some cheap P4 backpacks (US$17-18) fit well and reuse stock P4 packing foam. That's exactly what I was waiting for since bought my P4 weeks ago. I wouldn't expect high quality for that price tag. I bet these nylon backpacks (or similar) are available in ebay/amazon soon or later.
大疆phantom4精灵4无内胆背包双肩防水无人机外包外箱外袋配件
大疆phantom4精灵4无内胆背包双肩防水无人机外包外箱外袋配件