Who is the realistic target then for Shattenkirk?
If he's extended for 5-6 years at 6 million obviously the return should be more.
From Boston there's Spooner (lefty) who probably should be playing C but isn't. There's also Lauzon if you want a high end LHD prospect. It will be 2-4 years though before Lauzon hits the NHL. There's also Alexander Khokhlachev "Koko" (lefty), another 22 year old prospect who plays Center.
From Edmonton there's RNH, 22 years old (lefty) Center with 56 pts twice. Draisaitl, 20 years old, (lefty) another center but probably pretty hard to pry him out of Edmonton. Yakupov, 22 years old (lefty) 33 points is his high and at this point he really looks to be a 3rd line player. There's Anton Slepyshev, 21 years old (righty) winger. Griffin Reinhart, LHD, 22 years old and doubt they part with him.
From Detroit there's Evgeny Svechnikov 19 year old lefty winger. Anthony Mantha, 21 year old winger (lefty). I don't see any way they would deal Larkin. There's Nyquist, Tatar, & Helm. Helm would be an ideal 3rd Center.
From the Islanders there's Ryan Strome, 22 year old Center (righty). Mathew Barzal, 18 year old Center (righty)
That's at least some potential targets.