Pretty impressed how well that one turned out. Used SUNLU TPU in yellow with 200/50 degrees Celsius at 20mm/s speed on my Voxelab Aquila (upgraded PEI bed and DirectDrive, also used Filament drybox).
This filament to be exact:
Angebot: SUNLU TPU Filament, 1KG Flexibles 95A TPU 3D Drucker Filament 1.75mm Maßgenauigkeit +/- 0.03 mm, Hohe Liquidität und Elastizität, 1KG（2.2Lbs) Spule, TPU Filament für FDM 3D Drucker,TPU Gelb https://amzn.eu/d/7H5TLjr
Would it be possible to embed harder plastic bumpers/reinforcements from PETG or PLA inside the walls? I feel like that could make something like this even more useful
Probably. You would have to design a model like that before printing. I would leave some space in the corners and design some pieces that fit exactly in there. Then print these PETG pieces at first and the TPU case right after. When it reaches the point where the gaps would be closed the print needs to be paused and the cornerpieces inserted. Then resume the print until ready.