I can't speak for Lionel's solution, but I did this as a "proof of concept" (AM trucks, SHS hirail wheels and couplers) and it ran just fine on S-Trax.
Once reequipped with scale wheels and Kadee's, I have no trouble even on my rickety code 100 track. I've since regauged the original trucks, but seeing they make the car sit too high, I'll have to try to find a use for them elsewhere, eventually.
I guess I don't understand why Lionel didn't take the simple route and duplicate what other manufacturers have done.
I guess maybe the question should be: Are spinning endcaps worth all the grief?
Well, here's hoping the issues will be straightened out on the next run of hoppers and the 57' mechanical reefers.
It's becoming pretty tough lately to convince some folks the scale side that Lionel/Flyer's worth a look.
But even with all the problems, once they're fixed up, they do look pretty good in a train, (scale AM trucks, Kadee's) as Tom Hawley's cars do on the South Eastern Michigan S Gaugers modulars at this year's NASG convention:
Rusty