This idea is as old as Oak timber's, or Steel plumbing pipe or whatever else the guy had on hand.
It'd really be fancy for a Mariner with the Shift & Throttle in the same lever.
I raised an old Cedar boat from Salt Water. It's lever stuff was rotted away. I replaced it with a Cable Helm.
I never understood how a guy could get used to a stick moving for&Aft to turn the boat Right&left.
But as a fly fishing guy I know it'd be nice to get rid of all that helm stuff.
This 'thing' could be built in an afternoon if you had all the stuff in your barn. Then you'd know if it's for you or not.
Extensions for your outboard Shift/Throttle lever have been available for a long time. Lot's of River guides use those things so they can stand and negotiate a river. Standing in the back of a boat, diving between rocks etc is a Scary thought eh?