And Merry also got armoured in Rohan, with a leather jacket; Aragorn and Legolas were equipped at Edoras before the battle.
Pippin was last out of the blocks but may have come out with the best armour, being fitted out in Minas Tirith kit. That was a haubeck of rings too and a helm. So still no plate armour.
Even the Witch King wore a hauberk. Which implies mail to me. And surely this is the one being (other than maybe Sauron!) who would have qualified for plate protection if it existed?
I can't see any case for plate armour: but then I reject crossbows too - so they wouldn't be in any game I was in.
Of course, if you want to go with this, you will. Enjoy. The 5d protection and 15 Load seems a logical extension.