RS is not certified for over 500W nominal motor to my knowledge. Fox E-certified, Suntour, And a few models on Manitou (Mezzer, Mattoc, Machete Pro) are your best bets for a manufacturer backed fork with a more powerful motor.
170mm thats cool, tbh I did not want to go bigger than that really.
Are there any forks certified for 1000w+?
I assumed the new RS Zeb's might be certified for normal ebikes but I was not sure, to be honest just up the road from me there is a suspension tuning company called TF tuned. They are (in the UK at least) regarded as the best in the buisiness they rose to popularity customising stock Forks for use by the top teams and riders on the world cup Downhill scene.
In the most extreme cases the tuned version of the fork/shock shares very few parts in common with the original product. And the certification will be from them.
So it was in the back of my mind to go down that route and let them deal with the suspension geo and set up. But this will be decided towards the end of the build process when every other part is ready, which may be a while yet lol. Or during that time I may see a deal on some ebike certified 38's or something which I would snap up.
Manitou's are less common over here than they used to be and I want to limit the parts I am importing as much as possible. Especially with Brexit and other current world events it actually makes more sense to purchase from the US than it does from Europe (especially with help and advice you and Watt Wagons, and other guys that use this Forum have already given me) but I still want to limit Duty and Shipping as much as possible. And my budget kind of means that I need to build it in sections over a bit of time lol.
First stage being the Frame and Electronics. maybe rear shock
This has the added benifit of if I have major issues with my current bikes motor/electronics or even frame I could get something working quickly! as it is my main transport. And they are the parts I can not magic up next day.
But touch wood this will not need to happen and I will have a brand new bike plus my original mk1 Ultra project in a years time.
One other question will it accept a 44t chainring happily?