Hats off to everyone tries to improve stuff and experiments against the grain.
This is how things advance.
If we are talking about the same thing... 3kw and + power the logic of chain on an angle is what remains to be seen. Before we would easily say those bicycle cassettes would taco first. Now Mike's gone and made a custom cassette that won't taco.
How long any metal and chain will deal with being at the wrong angle is what remains to be seen.
So correct me if I am wrong, the modern day dere is made to work with 9-11 speeds usually. They were also meant to be used with 3 chainrings at the front to keep the chain in line. Anyone would tell you at 150w or whatever we usually pedal how bad it sounds when you get this wrong or take a huge body weight step and do this wrong. Then modern day stuff has start going single fronts because found they were almost always using one of their fav and wanted to save weight complexity.
Anyone who has ridden 1 x 9 or maybe its just me knows that once you get out to that granny it still rubbing at an angle. And that's around 200w cont.
For people who have run 3kw what is the least amount of teeth you can do it without skipping? this would be great data. I get skipping for example on 20t still with any derailleur (spelt right?) off the shelf. They all feed from 6 oclock position half the teeth so only 10 bicycle teeth taking the brute force.
The only way I can get 20t to work is by wrapping the chain around to feed the chain perfectly to 75% of the teeth. In this case 15 teeth engaged.
so that I guess would mean if using modern deraileurs with a 30t minimum chain might be ok if it feeds perfectly in line. A small misalignment will be self destruction.
Now lets line that 30t up as out fast as possible next to the dropout. From there you can start building out ward taller cogs.
I have only tried this briefly because I am not an expert with deraileurs (hate this word) all the springs and lengths are made shift across modern cassettes. If someone can make them shift from 30t to 40t somehow in this position. Hats off.
I can only assume with this that a custom deraileur is needed or you need a hell of a lot of patience to get the increments to work.
Last but not least with 3kw from zero to 60kmh changing gears seems ridiculous. In a race or even a fun bit mixed terrain, holding off power to shift will be a very slow process. You have to also stop and hope that you can hear that your change sounds clean before reapplying 3kw or else self destruction.
On road boys with long open roads might find this more beneficial. I am sure it will be great for some. For me the motor is efficient in that it never overheats, it rarely needs 3kw for long.
I'd still love two gears for zero to 30kmh and 30 to 60kmh. I just don't think derailleurs were designed to do that large a gap of beneficial changing in our specific application. bafang or small block yes. 3kw not really.
7 speed is the right chain from my experience. I can strongly recommend Connex wipperman 7e8. Longest running chain I've had. Although it did at the end with dirt mud grease build up start to dislike single speed cogs enough to want to hold on for too long and wrap up and double over and self destruct the drive train.
7 speed just works through both off the shelf tensioners and single speed cogs chainrings like spb cyclone. Go thinner more of that jamming on the thicker cogs, go thicker and tensioners and deraileurs wont let you get some single speed chains fitting through especially the izumi track single speed chain I got with some ridiculously wide connecting clip.
I do really look forward to Cheekyboke proving me wrong with some video especially
I guess I don't see the "avg" eBike market picking up a LR Small or Big Block. People are constantly asking me about WTF I have going on, but it's not for the "avg"! I'd imagine everyone with this kit is thinking the same. Once your human power is <~20% or less of total power, there's little to no reason to reduce the motor to human cadence. These last couple pages have made me quite happy, as a few of the "difficulties" are going to be worked out with the #219 final drive. Let it be known that #219 is good for 20hp(~15,000w), ie plenty! 
