I like the approach of bringing him to tour a few schools that he likes. Then have him ask the admission officer about the school’s expectation toward grades, ECs, etc. It may help if he sees something more concrete in terms of goal setting.
To help a kid be self-motivated, sometimes it takes a few initiatives and trials on the parents’ side. I remembered when I was young I was minimizing my efforts and maximizing my happiness fooling around. It was my mother who told me that I had two choices: either work in a local factory (for the rest of my life) or work hard and get into a decent school. I chose the latter. I know that was not a sound approach, but it worked for me.