The current electric bike issue is the same old one, range. Or perhaps the relationship between range and weight, getting an energy-dense battery is like coming up with the rocket fuel capable of escape velocity. It's getting pretty viable if you can plan your stops to recharge and such, but I bet it would be an exercise in hypermiling, which I don't really mind doing sometimes. The torque kinda begs for traction control, as lowsides seem pretty easy to come by otherwise.
It may never be needed but I'd love to have a diesel/multifuel/electric hybrid bike. Something kinda low-slung but capable offroad like the TW or a modern scrambler. It would be harder to do but I'd prefer to have either motor power the rear wheel, as opposed to using the engine as a generator. Regenerative braking would be very handy on downhill sections, especially steep trails. The weight would be crazy but you'd have tons of torque and I think the TW is a testament to getting by with relatively low ground clearance offroad. If you could somehow make the weight manageable and still have that clearance, it would be awfully useful. You'd lose some offroad capability but a sidecar rig seems like a good candidate for a hybrid. Wouldn't be the first diesel hack by a long shot. You'd need more suspension than a TW offers regardless I'd think. If I ever get good at fabricating I'll let you know how it goes.