There must be some reason a bob with a hub motor is undesirable? I want to build one but I might be missing something...kinematics or something? I can see the rear wheel being pushed outward while turning...is that it?
I built up one 7 years ago with a Golden Motor and a 48v/11Ah Duct Tape battery on a Yak. Used it primarily on my Townie. Carried the battery on the trailer along with a conveniently sized cooler to do chores and get groceries. It was powerful enough to get me up the steepest streets in town which are pretty steep there actually. Took a few 25 mile jaunts with it but it cut out at 20mph and had a lot of parasitic drag trying to go any faster unless you were coming down the aforementioned hills.
Never had any handling issues but was sensitive to giving it much "gas" when doing a sharp turn. It helps to have some weight aboard like the battery as it can tend to be a little light traction wise without any.
It is a great concept that never has gotten there yet, if it ever will. But the ability to have an e assist that you can ditch easily or swap to other bikes in the fleet is definitely valid. Ride to the trailhead, stash it, ride, then hook back up and pick up the groceries on the way home.
Yeah I tried it with the notion of hauling trail work tools; there's just not enough weight over the trailer's wheel for traction off-road. Even with an aggressive (and hard to find) knobby tire it was always spinning out. (very hilly terrain where I ride) I did leave the battery on the trailer though, I use it as a spare for the mid drive via an extension cord.
That is similar to my old setup MP. I didn't try and use it off road though much as you say it doesn't have the best traction which is mainly due to the fact that it bounced on anything bigger than a golfball enough that it would break traction just and start spinning so that when it contacted the ground again you would feel the loss of traction. For that purpose the above setup would be better.
I used mine primarily on pavé as that was my need at the time and it held traction well on the smoother surface as long as there was some weight in there as mentioned. I am sure you used yours enough in that type of situation to know this to be the case.
I am still not sure why people that have never experienced something like using a pusher trailer think that it will just handle like crap and make for funniest home videos. I put over a 1000 miles on mine and never had anything close to a mishap handling wise. I also use a front hub motor which many think is the fastest way to land on your face but that is also a myth if the proper installation and use of it is perfectly safe and sound.