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Anyway, starting to shop for my next focus EV and want to do the 2018 RS body parts (and eventually the interior). Since the RS is AWD. The rear spindles are bolt on, unsure if I could also use the same axles as up front but (once the warranty is up) I'd like to add another motor for the rear.
That will be a packaging challenge, but is potentially possible. In a quick look it appears that the front and rear hub and bearing designs are completely different, but if you are very lucky they might use the same outer CV joint or at least the same length and spline of the stub axle... but I think you're heading to an auto wrecker to get samples of the front and rear halfshaft assemblies and maybe hub assemblies to check them.

Also, the stock track is different between front and rear:
Front track: 1,554 mm (61″)
Rear track: 1,534 mm (60″)
(from The Car Guide)​
That means that each halfshaft from the front would be 10 mm too long for the rear, plus or minus the effect of being installed in different hubs (if they fit). That might be within what the plunge length of the shaft assembly allows, but it would be very bad if the shaft bottomed out.

In most EVs (and this one looks typical) the motor is off-centre, so the differential is reasonably close to the centreline of the vehicle. The end result is usually two different half-shaft lengths (which is okay) and a motor sitting too far to one side (usually the right-hand side) to fit between the parts of the rear suspension (which is an entirely different design from the front).

... second motor would need a controller. (Unsure if there would be a way to grab the front drive controls and port them to control the rear as well).
The controller for the rear could certainly pick the accelerator pedal position off of the CAN bus, and perhaps you could get some information from the front controller, but just applying the same power to front and rear will never be optimal.

Ps. Magna. The company that makes the focus EV drivetrain, I found in one of their documents that their is a larger motor option ford didn't go with. Perhaps with the right contacts that larger motor could be sourced for both front and rear giving this car the nuts behind the RSE badge.
I wasn't aware of the extent of Magna's EV product line until I did some searching after reading your comment. The problem is that no matter how broad their product range, you can't buy any of it unless a vehicle manufacturer has chosen that product and used it in their production vehicles. Magna only supplies OEMs (and presumably distributors with items corresponding to what they sell to OEMs), not individual hobbyists.

But seriously I'd run two leaf motors out back if I could figure that out. Or four if possible.
That would be great for power (and for traction and stability management) but the weight and bulk of those motors - plus their gearboxes - adds up quickly.

Putting a motor in the rear of a normally front-wheel-drive vehicle is often proposed in this forum, and rarely if ever built. The Focus RS is a better candidate than most, because it already has driven rear wheels - that's a huge advantage. A full EV is certainly more practical than the hybrids which are usually proposed. I like the idea, because the result could be very desirable, but the reality is that there are many practical issues.

One disadvantage of the Focus is that the EV is a straight "compliance car", built with as little change to the base gasoline vehicle as possible, so it has no provision for battery under the body, beyond the original fuel tank space. Vehicles such as the Leaf and Bolt also share a platform with gasoline cars, but have a different floor to allow for a battery pack which extends further forward.
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