This is often talked about but rarely accomplished. The easiest way to do it is to take a FWD car with a AWD option, add the AWD rear subframe and add a motor to that.
The main issue is interfacing the two drive systems. With an auto that's fairly easy, but that means the engine has to be idling all the time in EV mode or you'll kill the tranny. It may be possible to add an electric pump to circulate fluid while the engine is off, but I have yet to see this actually done.
If the engine has to be idled all the time, you'd probably get better results from a manual conversion and EOC.
But yes, I'd love to do this to my VW T5, add a big electric motor (no need to use a Tesla motor, plenty exist off the shelf), and have 800NM plus great economy from a 2ton AWD van
It has an AWD version so the conversion is fairly straight forward. However, it's a manual and it's very hard to come up with a fool proof way to interface the electric motor with a manual trans.