As for the chi-rho texture, I think there is a banner for someone's mod (I don't know who) that works on shields. Other than that, I can't really help.
I don't know for sure. But I'm almost certain at least some Romans use it. And the Roman shields are used.
Also, I would doubt it historically because, by that time, (and I'm basing this off of nature) Rome's enemies probably would have understood the weakness of the armor (if any, since it was some damn good stuff), and also because the armor was given up for its price and maitenance cost. I think the latest recorded usage was in some statue of Constantine I in some time around 300ish, but then again I'm not sure. I'm almost certain it was replaced by some later form of Hamata. Gladii, as well, I think were replaced by Spathae like Deepeeka.