S. Damage Threshold / 3E Damage Resistance / Runequest absorb-X-points-YY%-of-the-time would be good. That is, "drop all damages from slashing weapons by 2", for example. Avoids the "nibbled to death in shiny full plate armour by a horde of xvarts" syndrome.
A. Agreed! Sadly technically very difficult to do in the BG2/IWD1 engines, and the workarounds are unlikely to work well enough to be worth it. Will probably be implemented in a (hypothetical) IWD2 version of the mod, since the IWD2 engine has support for it.
Q. Can I disable the movement slowdown from heavy armour? It annoys me.
A. Umm... yes, but not easily. Watch this space. Won't be a standard option, since I consider it part of the balancing of the mod.