First, let me say, I am a Bengals fan, but trying to look objectively at this.
Under today's rules, no doubt, 100%, this is a penalty.
If you watch the video and try to imagine faceless, nameless players without the jerseys to eliminate bias, here is what I see.
I think the best angle starts at the 0:16 mark of the video and the ball has just gone through the WRs hands while he is at the peak height of his jump.
At the 0:19 second mark, the LB enters the screen on the left at the same time that the WR lands on the ground. The key is to look at the positioning of the players at this point. The LB is bent at the waist with his shoulder level around the WR waist area as he is landing, and looks to be within arms reach of him (say 3 feet). The WRs momentum, and possibly natural instinct, causes his knees to buckle and he lowers his head right before impact (still at the 0:19 mark of the video, also at the 0:32 mark from the back angle). The LBs shoulder level does not change, still at the original waist level of the WR, which is now the head level due to the WR reaction upon landing. Contact occurs at the very start of the 0:20 mark and the LBs momentum continues through the hit with his shoulders at the same level as when he started. There was no upward motion or launch into the WR.
I truly believe it is player reputation alone that is causing people to say this was intentional, and maybe that is deserved. But if you strip away who was involved and look at the video alone, this has to be the exact way you would teach a LB to hit a WR in the last seconds of a playoff game. His only job is to assume the catch is made and he must dislodge the ball, risking the potential penalty under today's rule. The LB cannot allow the WR to make the catch and continue the run. If he wanted to, I truly believe he could have killed Brown (literally) on this play had he launched upward (similar to Terence Garvin's hit on Huber a few years ago, by the way), but he didn't. Now, if he is that good of an actor to make it look like he wasn't trying to hurt Brown but really wanted to, then maybe he deserves the Academy award, but I don't think Burfict could pull that off.
Had the Steelers kicked a 49 yard FG to win the game, I would have no problem with the end of the game, but we won't talk about what happened next here. What I think is incredibly ironic is, had the fumble not happened, they would be preparing Burfict's and Jones' statues for out front of PBS.