I recently found out that you can apparently reduce the travel of 8" DH forks such as Fox 40 to 6". This raises the question: would it make sense to do this for ebikes? I like dual-crown forks because they are stiffer and heavier and somehow seem more suited for an ebike, yet I don't see this approach in the wild as most people seem to be happy with single-crown fork such as Fox 34 or Fox 36.
eBike manufacturers seem to think that single crown forks are strong and durable enough. Double crown forks are likely too heavy and overbuilt for use on an eBike.
Can be done? Yeah, sure. Why? Depends.
Depending on how the fork works on the inside, reducing the travel is pretty easy. You need spacers and sometimes a small spring.
What are the caveats? Well, less travel for one and a reduced chamber on the inside. If your fork suspension is by air, then well my friend you will have to tune the pressure pumped in the fork, as it will compress way faster than before. On some cases you will need to take a little bit of fork oil out, so you won't get hydro bottom the fork. Also you'll be surprised how much the weight balance would shift with a heavier fork.
The ride I've seen with eMtbs is like softcore enduro. They appeal to me in the sense that you don't a truck on a lift and you can ride longer. But you pay the weight penalty and the autonomy.
I was a Downhill Riders back in the day and let me tell you I do like those double crown forks, I feel more confident riding them but the materials used to build bikes nowdays are amazing, super strong and for most riding is OK.
If you ride like Josh Bender, I believe that Avalanche Suspension are still on the market.