Needle Hotend for nonplanar printing To minimize retractions and travel when printing several objects, some slicers produce gcode for sequential deposition when each object is built in a traditional manner bottom up layer by layer before starting a new object. Of course, there are limitations caused by the hotend geometry  we might even do things like spiralizing contours of a single object. This has also potential for other tricks like producing interlacing layers for better layer bonding etc. I wasn't able to find any ongoing work on minimal geometry hotends. Any links? And what might be the challenges in making one? heatblocks and heating cartridges are out of the question but nichrome wire and a fast PID heat controller might do the job.

The site is not well-suited to crowd-sourced invention, but the drawbacks to your suggestion are (I think) on topic.

The hotend has two main tasks. Accurate control of extrusion, and maintaining the desired volumetric melt rate. One factor which influences extrusion quality is the size of the melt-zone - generally, you want this to be as small as possible because rigid filament is easier to extrude/retract without ooze/stringing. Equally, the melt zone needs to be provided with a thermal mass (physical or virtual) to stabilize its temperature under extrusion.

Whilst it might be feasible to prototype your concept quite easily, it is likely to be expensive in volume - and there is no great direct advantage. So this is a concept which might enable an area of research but it doesn't look like a development objective with its own intrinsic value.