How hard or impractical would this non-ecomod be on an Insight?
 

I am curious about how hard it would be to add backseats to an Insight. I am not sure if this has been done before, but I'd maybe expect someone who does Uber or something to add backseats to an Insight.

There wouldn't be enough legroom or headroom.

Unless the passengers are the size of a bag of groceries, it would need to be stretched, like this Metro:

https://i.imgur.com/408Tt.jpg

The was built by Dave Cloud, who was famed for another vehicle. He said it wasn't too hard a stretch; but the Insight is aluminum instead of steel. You could probably do a lot with the OEM grade adhesives available today and save a lot of welding.

It seems people avoid welding aluminum, but I don't know why. The kids in my high school group that welded the electric car together with zero prior welding experience managed to get it done with a MIG welder. The sole brake plate (stopping is an afterthought when figuring how to win a race) only broke off once. I advised the driver on the radio to not touch the brake pedal under any circumstance, and to proceed racing as if there was no brakes (which was accurate). I wonder why PGE stopped sponsoring that race series?

I avoid it because my welder can't do it.

You could remove the rear hatch and install a rumble seat!
https://en.wikipedia.org/wiki/Rumble_seat

What if you just gut out the trunk?http://images.gtcarlot.com/pictures/59864144.jpg

I helieve the primary reason to not weld aluminum is the tricky state change to fluid. Get too hot and it turns to a water like fluid and runs all over the place, at least for me. Chill plates help as does flooding with gasses. Great thing about MIG is the area that gets hot is quite small and is flooded with cooling gas.

There's basically no way to do it without rebuilding the car completely. It's not like a CR-Z. It was designed ground up a 2-seater. The foot well is taken up by the gas tank. There are structural braces across that area. The hybrid battery is in that spot. The roof slopes down there. You might as well build a new car.

Uber also bans cars past a certain age, and no first gen insight is newer than ~16 years old at this point.

Besides the legroom and headroom issues, finding a good place to anchor the seatbelts may also prevent the fitment of a rear seat to become suitable to an early Insight.