Great mod! My fingers thank you. This should be in vanilla.

Would it be possible to add this to the vehicles? And/or keep the auto-move function on while we turn left or right? To cancel only when we tap the the bound Stop key or the back-up button?

Hey there, glad you like it!

I'm not sure how easy/hard it would be to have a similar function for vehicles. Currently I'm not able to work very much on it, so I won't be attempting that any time soon sadly.
Perhaps someone more familiar with the modding API could find a solution.

I like your idea for controlling vehicles that way, would be really easy to get around just tapping left/right and still having velocity in the vehicle.

LOL.. FYI.

https://mods.factorio.com/mod/Vehicle_Cruise_Control

This mod works great for walking, vehicles and spidertrons:

https://mods.factorio.com/mod/Kruise_Kontrol