Last 30 goal season by a defenseman, Mike Green.
And it was 1992-93 the last time before that, when Kevin Hatcher did it, and obviously scoring was much much higher back then. So, it's only happened 1 time in the last nearly 25 years, and it's incredible he's doing it in today's NHL.
Actually, only 8 D-men in NHL history have scored 30 goals in a season, and it's only happened 17 times, ever, with the vast bulk of them happening in the 80's and 70's, when scoring was obviously much higher:
Bobby Orr (5 times)
Paul Coffey (4 times)
Denis Potvin (3 times)
Doug Wilson (1 time)
Phil Housley (1 time)
Ray Bourque (1 time)
Kevin Hatcher (1 time)
Mike Green (1 time)
So yeah, Burns is much closer to doing something incredibly historic, and I'm really glad he got his goal back. Right *NOW* he's tied for 28th place in the "Most goals scored by a D-man in 1 season in NHL history". He's also the oldest player to be on that list, at 30. Al MacInnnis had 28 when he was 30, but everyone else was generally in their early 20s when they scored that much. Coffey was the oldest to hit 30 goals, and did it when he was 27 in 1988-89. That makes what Burns is doing even more historic, IMHO.