I am really against trading him because we are building a team (currently) around the idea of having two stud offensive defensman, and either Burns or Karlsson could fall from grace at any point in the next couple years, if we assume Burns is just having a down year and has not already started his decline, so we need Merkley to fill those shoes.
No idea if he will ever be able to fill those shoes, but he is the best shot we have at doing so.
Also, from a value standpoint, I think he will the make the NHL soon, and will be worth more having proved the ability to make the NHL than just being a prospect racking up points in the minors.