I've been thinking a bit about this and a very easy way to implement something similar to Damage Threshold is by using the currently existing feature of 'Normal Weapon Resistance'. We had this feature in TES4:Oblivion where an opponent could be partially/fully resistant to normal weaponry. Not entirely sure if the 'Weakness to Silver' has also been retained (or if that one was only in TES3:Bloodmoon).
At any rate, these two types of weaknesses/resistances could be implemented quite easily to provide a form of Damage Threshold. Power Armor could have a 'hidden ability' in that it provides 100% Resistance to Normal Weapons. So all the devs would need to do is put a checkmark on specific (powerful) weapons to make them the equivalent of 'Magic' or 'Daedric' weapons; and as such being able to penetrate (for instance) Power Armor. The rest of the weapons would be completely ineffective against such armor.
If the 'Silver Damage' is also still present in the G.E.C.K. (as it is a modified TESCS after all); you could even have a more diverse way to handle things. Maybe even utilize both features so some weapons would have a normal effect (5mm Minigun); whereas others would be highly effective (Plasma maybe?).
This would translate as weapons like the 10mm pistol (that would not have the checkbox) to be completely useless against an opponent in Power Armor. However, the Minigun (that could have the checkbox) would still be effective. Plasma weapons (that could have both the 'Bypasses Normal Weapon Resistance' and 'Silver' checkboxes) could have an increased effective capability to penetrate Power Armor.
Just throwing it out here, as a lot of people had been discussing the term 'Damage Threshold'; so (after my cup of coffee) tried to find an easy and effective way to implement a similar mechanic by using existing options.
But in short, I too want to have Damage Threshold back. This would force a player to actively change weapons depending on the type of opponent in the game and not killing everything (including opponents in Power Armor) with a simple pistol or Nailboard.
Greetz,
Milt
