With the standardized latch system you can fit a car seat in about 2 minutes. The main issue is when you transition out of the clip-in car seat to the larger seat at around a year as you certainly wouldn't want to have to lug one of those around at the other end.

That said it's a solvable problem with some thought, engineering, and standardization, but you are correct in saying it won't be solved until ride sharing EV's are out of the early adopter stage/commuter stage.