Needle Hotend for nonplanar printing
A conventional hot end needs only to be obstruction-free to the desired printing height on two adjacent sides to achieve what you want. The only other requirement is to be able to tell your slicer in what order you want your models to be printed.

For example, if your hot end is free of obstructions on the front and left sides, all that you need to do is lay out your models in a rectilinear grid, and tell your slicer to process them front-to-back, and left-to-right.

I have thought of doing this myself. By mounting my E3D V6 hot end as low as I can on its carrier, I should be able to print models up to 50mm in height, and only spaced 20mm apart. I may have to forego part-cooling, but I mainly print PETG without part-cooling, so no problems there.