Yeah, I didn’t touch on fore-aft, but I think it is very worth including along with lean. Each direction of motion offers something the other does not, and I would probably not like going back to lean-only.
I don’t know if the F-A is really the key for back SI issues, but it can’t hurt there and pays off for nearly everyone I have seen. The only common negative is those that like to sprint hard on the trainer and don’t come to terms with the motion. I am used to it as are many others, so I think the benefit it offers in the 90-95% of seated riding is worth it for a majority of riders.