Motors in front forks
Thorn's response in the current journal is the only one any manufacturer can give regarding something they have not manufactured and/or tested.
Front forks are not useually designed for retro-fit motors and serious injury can occur if the forks are not up to the job. (read Trevor Jarvis' article in a previous journal.)
My advice would always be to consult an experienced frame builder regarding the need for new forks suitable for a motor.
It's always worth considering a new machine as the number of E-Tandems being manufactured is increasing.
To back this up, there has been at least one, possibly two front fork failures in the West Country Tandem group due to an electric motor on the front forks. The one I know about occurred after a year or so of use ...