If there was ever a player who was a prime candidate for one of those Guardian caps, it was him...

With what we know about repeat concussions (i.e., having one makes you that much more at risk for another, and the risk increases even more with each successive), I could see teams/the league mandating them for players like Tua who have definitely had repeat concussions - it could get to a point where it's 'wear one or retire - your choice'.