a tidy conversion, but overall pretty pointless.
the 4 door is no moe practical than a 2 door, the boot is no bigger, there is no more headroom or legroom. the 4 door e36 kind of made sense as it is actually a different bodyshape to the coupe rather than just having a couple more doors.
having only 2 doors on my m3 has never been a practical problem, adults, children, child seats etc all fit in fine through a 2door doorwith the seat tilted forwards, and as i'm not often used as a taxi, having to get out to let someone out of the back is hardly a regular chore.
i also think the rear door opening looks a little strange, i think if i was doing it similar i'd go the same way lancia did with the integrale, and take the door opening right to the edge of the arch like so

just looks neatr to my eyes than having a second line following the curve of the arch.