I got two tips from readers.
Please note that my current focus is construction of the bearing.

Different PCB windings;

The advantages of improving the PCB windings are;
    - ability to replace rare earth magnets (neodium) with ferrite magnets
      ferrite magnets are 2 or 3 x times less powerful but much cheaper 
    - it might be possible to go from a four layer PCB back to a 2 layer pcb (reducing costs)
    - ability to achieve higher spinning speeds

Keith reinolds pointed out that a Faulhaber winding is more efficient than the bugeja coils or the improvement outlined by atomic14.
This is outlined here.
A linkt to a review paper is provided by gravis https://ietresearch.onlinelibrary.wiley.com/doi/full/10.1049/iet-epa.2020.0141

Mini laser prism scanner

It could be useful to make a very small laser prism scanner. There are applications in imaging, communication etc. as outlined earlier.

Two things are of interest;

You can buy precise micro prisms, which have dimensions around 1 mm.

https://www.neg.co.jp/en/assets/file/product/ep/micro-prism.pdf

Magnetic levitation

Wikipedia provides a good overview on magnetic leviation.
You might be able rotate the prism if it is made from a diamagnetic material.
Lawrence kincheloe pointed me to an article which does this for a pyrolyte sheet,
https://pubs.acs.org/doi/10.1021/ja310365k

I can also imagine you trap a rotating prism with a magnetic trap