At this time of writing, I'm still going to go thorugh with the soon-to-be-designed dual motor Tetrinsic, but I'm still not happy about the length and height of the current solution. While the active length of 63mm makes sense as all 4 fingers can ergonomically exist in the resulting quad-Tetrinsic area, it only accounts for 54% of the total length. The thickness of 28-29mm is also limiting, and ideally Tetrinsic would be half this.

Other than width, the main ergonomic issue I need to engineer for is to obtain reliable fingertip grip whilst having a very low friction sliding surface, even when pressure in excess of 100gf per finger is applied.

To have a chance of meeting an under 15mm thickness target, a potential solition is to give up infinite-scroll and off-the-shelf hardware for a custom linear motor:

Unfortunately, I think the bigger issue is developing the software for Tetrinsic and mounting strategies, so right now I need a development solution and not an ideal solution.