The S5 swap is interesting for being the first, and much kudos to those involved for reverse engineering all the stuff to make it work, but its a big compromise with the batteries taking up most of the rear of the cabin. That was done to keep the original quattro drivetrain - in the vid you can see the Tesla motor attached to the original gearbox.
An 8 is actually a decent recipient for EV stuff because it is so large, although keeping AWD would compromise range, simply due to packaging constraints.
My plan would be based on a Model S, and I'd basically replace the rear subframe with the complete Tesla rear subframe - drive unit and all. With the fuel tank removed there is plenty of height for the motor, and the Tesla subframe is a very similar concept to the D2 / D3 unit.
To try and do AWD would be a bit more of a challenge since the Tesla drive unit is quite wide so may be tricky to fit between the chassis legs. I'd need to get my hands on one to try it though.
Since there is no driveshaft or exhaust, at least two, possibly three Model S batteries will go under the back seat.
Up front, I think another 6-8 batteries will fit in the engine bay, although AWD would reduce that to probably 4.
For even more range, a couple more could be fitted under the boot floor. Of the 16 batteries in a Model S, I reckon 10-12 could be fitted in to an 8, giving a range of probably 200 miles.
For electronics, all the chunky stuff (and an electric AC compressor) can go in the tunnel since that's empty now. There are 3rd party control units available these days which can make the drive units, batteries, charging system etc run without the rest of the Tesla being attached, and which can output canbus to make the recipient vehicle still work so effectively the rest of the car would remain as-is. The ice drivetrain just gets replaced with electric.
Simples...
