the New shifter and BSR work better than the old steel trigger + AW3.

Asian Ebay Had a 5 speed hub wheelset for Bromptons, Using the 2 speed Driver,
so 10 'speeds' is Possible..


SRAM Dual Drive has a unitized shifter for internal 3 & the cassette 8,9,10.

you are free to try some mechanical solutions on Your own..

The German Engineers at Rohloff have designed 3_3 speeds
and a Big range drop gear to work in sequence shifting thru 14 gear ratio combinations.

[actually some parallel with Schlumpf mountain drives, in that the high range gear set,
is used a second time through]

Maybe the single lever twin cable design is a Good senior/post grad project in your Mechanical Engineering Degree Pursuit.

/