For most shocks a little foam goes a long way, having the electronics be bolted to a cushioned box or having the electronics laying in foam (with appropriate cooling) helps a lot.

Source: I cushion my robots this way, haven't gotten to the ebike yet.

The whole is mounted in a trespa box in such a way that there is a few millimeters of shock mount in all three directions (very high density foam) and all empty spaces are completely filled up. That box in turn is then mounted to the frame again in a similar way, I tested the whole using dummy weight and the accelerometer in a phone to see what happened when jumping a pothole at speed (which is about the worst that you could do to this bike) and it came in well under the limits and also tested it on a very rough path to see what it would do when subjected to vibration. The front fork is a very nice 'Fox' unit with adjustable springs which have been set to be in the middle of their travel range when the bike is fully loaded and so that it never bottoms out even under the worst conditions.

On the whole it isn't perfect but good enough for many years, I've run this setup for a year now and have once (at 5K km) inspected the wiring and the battery welds and everything seems to be holding up quite well. Things to be careful with: overpressuring the tires would reduce the amount of shock absorbing capacity quite a bit (and is definitely not recommended with tires this wide anyway), the rolling resistance of these is fairly high but that is just how they are designed. Then, obviously there is bumping in to things and falling at speed, which fortunately hasn't happened. But if it did I would immediately consider the battery pack a write-off in spite of being super well protected. I've done about 10K on it now and when it hits 20 I'll take the whole thing apart to see if there is any wear that is hidden from view. I'm mostly concerned with the battery welds and the wiring, those are the weak points, even with all of the wiring contained within the enclosure, routed carefully to never cross over any other wires and with the welds checked using a FLIR during a pretty rapid discharge (twice as fast as the motor could ever do).

The OP has mounted the charge controller and the motor controller to a piece of wood (which will flex a bit but not much) which in turn appears to be protected in only one axis (side-to-side) and is either free to move or rigid in the other two. The wiring runs 'cold' without any kind of extra protection through the wood that it is mounted on. The frame is unsprung as far as I can tell, which especially for the front is not a luxury on a bike this heavy, which makes bike+battery the unsprung weight (I think I see a saddle pin with a rubber mount so there is some flex there). That battery box may have some foam in it or some other suspension for the battery which is good.

As long as he's on good asphalt this setup will work, but as soon as you go on less perfect roads I think that it will give trouble over time. DIY stuff like this looks great on the day you build it if you don't build it for abuse, but exposed wiring is dangerous and vibration as well as the weather are going to be rough on this. I'm curious what it will look like a year from now if used intensively, and also how the wire runs are on the other side of that board.