once you start going electric do you really care about what platform? All the steering feel and fun is already sucked out of the car for battery weight and packaging. Seriously, one chassis would be better between two car companies. The more people that share one platform the better. It will speed up what EV fans want. Autonomous driving and complete removal from the actual driving experience. Chassis commonality will put all vehicle 'dynamics' into software people first, who will be able to 'tune' out any inherent chassis shortcomings.
shared chassis will mean larger parts commonality, charging infrastructure similarities, and hopefully price drops so those who really want an EV an afford them easier.
I hope the Toyota/Subaru EV platform is 100% identical. It would be good to have some more Toyota Reliability in a Subaru.