I'd considered going that route as a solution to part armors, so the plate helmet with chain shirt and leather arm and leggings would be:
Get a hit
roll a location
roll critical that ties to the armor in that location
But in testing it out a little, I ran into the problem that while chain/scale operate somewhat akin vs bash or slash, they operate very differently vs puncture. . .and that's before you get into things like Fire, Acid or lightning. . . for having a caustic liquid or gas tossed on you, chain is almost just something to slow you down without helping at all (if you get any protection, it's from the under padding worn with the chain). . .and you get similar variations between armors that would seem to lay in the same overall bracket.
I also end up making the system more ding or deadly. . .since the columns were armor types, the crit levels became modifiers ala a = -25, B = -10, C = no mod, D = +10 and E = +25. . .
The current crits are roughly 8% fatal, but balance out at C with like 3% on A and 15% on E. . .if you kept that average, the mods for crit levels would mean that A and B crits were never fatal, C crits remain 8% fatal, but D crits are 18% and E are 32% fatal. Admitedly you could use smaller mods than I tested with, but to make them small enough you end up with something like -5/-3/0/+3/+5 which starts to result in minimal variation.
I like the variations in result, though it's super annoying to have your 48E slash with the battleaxe on an Ordainer result in 01 crit "ding! +5 hits". . .things like that are not necissarily bad. . .sometimes people get shot clean in the center chest, just to have the bullet deflect off a St Christopher's medallion and cause a nasty bruise and a cracked rib rather than a fatally punctured heart.
The current crit system has 5 columns of 17 results. . .so any possible weapon vs armor combination could potentially result in a wide variety of attack table results, then 5 x 17 = 85 possible crit results. . . one of the things that made me finally abandon my "use armor category to replace A-E columns" was the fact that if your fighter wears chain mail for his whole career, he will experience 1/5 the amount of variety of results compared to the old A-E mechanic. . .and I think the vast variety of results is a plus. . .A lot of original RM1 people picked up and used each further iteration of Arms Law just to get new flavor text in the crits, as even with 85 possible results on each table, they'd had them repeat enough to get stale and wanted more new results enough to keep re-buying a full book just to use the crit tables in the back.