I tried yesterday with the following:
AC: 10 + armor bonus + fighting skill instead of Dex (not getting into details but you buythe skill from +2 to +6). Medium and heavy armor limit you skill bonus to AC, but grant damage resistance from physical damage of nonmagical weapons. Keep in mind that...
Well, that would add another step. You propose con+armor vs something like 8+stat+proficiency for a soak roll after being hit? The idea of player rolling their defense isn't a problem, but the extra step isn't exactly what I'm looking into; if I used that I would do something like a save vs 12 +...
TL;DR: For a limited-hp sword-and-sorcery people-are-monsters monters-are-rare kind of game, do you think that giving armor Damage Resistance (against physical damage from non-magical weapons) while keeping around half ac value, is a worthy compromise instead of trying to write up an Armor as DR...