For me, there's no doubt in my mind that Beaulieu will develop into at the very worst, a top 4 defenseman in the league. I've probably stated that more times than I realize. I expected him to pair well this season with Weber and while that didn't happen, I actually think it's obvious that he has top 4 caliber potential written all over him. He made the team quicker than other defensemen of the same age who will still find a home as 3rd pairing defensemen in the league.
Even most who are against him state that he has the skill but nothing between the ears. First of all, if you've ever heard him during an interview, he generally tends to say all the right things. He doesn't actually strike me as someone who is missing anything upstairs. I think it's unfair to label people like Eller, Beaulieu, Emelin, etc. who don make boneheaded plays from time to time as intellectually inferior in any way. Secondly and tied in with that, those who don't believe he will grow into his potential argue that he will be the same at 30 mentally as he is now. If that's not anything other than a simple hypothetical hypothesis, then I don't know what is. I can just as easily say that he will mature in those areas and may even find himself as a top 2.
My current expectation of Beaukieu and where he might fit on even a contending team? A top second pairing defenseman, or #3.