When did they start bringing Burnett down to LB on a consistent basis in nickel? I won't claim to clearly remember but that sure seemed like last year at best. And as far as being serious about it, Richardson was a UDFA. I would call that more of a flyer than planning to consistently execute a Nitro package.
You need the pieces to commit to anything. I don't think it matters that Richardson was UD, they identified him with a roll. Nobody in the league was really "committed" to it until ARZ and a couple other teams just last year. There was some experimenting in 2015 but nothing consistent. Dom was on it in 2013. I wouldn't use Burnett's activity as an indicator either because until HHCD solidified the other safety spot, we couldn't afford not having Burnett playing the only S spot back there. Dom gets a lot of heat for gauntlet of reasons but he would not be a copycat in this instance.