The plastic interiors started when Gould Inc. intoduced the I-T-E EQ III loadcenter about 1979,but I do have to admit the split neutral in those panels was a nice upgrade.
never had or seen a problem with a QO, plastic seems plenty durable, breakers clip on nice and tight, I really like the way that most of the buss is covered, keeps you from getting zapped by all that exposed metal...