Recently spent hours running a character to confirm something I couldn't find on the internet - and yes, if your armor penalty is upwards of 115%, then Nimble does literally nothing. Which is sad. And presumably applies to Body Weight Training as well.
And apparently I get 0 movement points in such a case, despite my character info screen saying my armor penalty is capped at 95%, which should still give me 2 or so movement.
I'd like a feat that affects the maximum, rather than current armor penalty, so that if you are wearing equipment with a total penalty of 120%, you can have an effective penalty of 80% and still have a few movement points. Alternatively, rather than target armor penalty, instead target movement penalty - say that slowing effects cannot reduce movement points below X, possibly scaling with strength. This wouldn't affect dodge, evasion or stealth, so 120% penalty armor would still nullify those skills, but it would prevent effects such as chilling from removing all movement points. If it scales with strength - or just requires a lot of it - then it would work for the build I'm looking at (superheavy armor + balor sledgehammer) without being available to every build as a means of taking the bite out of slows.