What Eco-Modding can one not do on an autonomous car that one can do on a non-autonomous car ?
Well .. All the 'nuts & bolts' stuff , Aerodynamics , weight , engine tweaking , etc ... all that 'nuts and bolts' type of eco-modding would be about the same.
The only difference I see to the 'Nuts & Bolts' ... would be that mods could be more accurately tested and quantified afterwards with an autonomous driving car ... far more so than a manual human could possibly perform ... The computer would be more able to repeatably drive / accelerate / etc ... exactly the same way to the millisecond ... 10 tests, 100 test .. etc.
IF the driving style is significantly user configurable .. like fonts and colors on my computer .. or the plethora of smart phone apps .. IF if reaches that level .. than being able to tweak my driving style algorithm .. I would than be able to tweak my driving style more precisely and more quantitatively and more consistently than would be possible manually .. and the fruits / benefits of such eco-modding tweaking / apps .. could be uploaded and shared to others .. on some type of common meeting site where people (who own autonomous driving cars) trade eco-modding data with other such eco-modder interested people.
IF on the other hand .. it's more like one only has 2 or 3 approved driving style choices .. and choose a destination .. than that makes driving more like being a passenger on a plane , bus , train , etc .. That would have reduced Eco-Modding capacity in the drive methods / algorithm part.