There are enough stories of taxi/uber drivers who basically only charge at superchargers getting 200,000+ miles out of their Tesla battery that slowing down charge speed to optimize battery life is a minor optimization at best.
What would be really nice is a better way of sharing a charger after you're done charging. My experience is that a Tesla supercharger is often too fast. On a road trip charging stops usually coincide with meals, but a charge takes less time than a nice meal does. The charge is done and idle fees start accumulating when you're halfway through the meal. It's rude to others waiting for the charger to leave it there plugged in. It'd be awesome if there was a way to have two plugs per charger, and a big green light to indicate that the first car is done charging so that anybody pulling into the second stall would get a full speed charge.