I was into a Markkanen trade when we were trading Brown for Lauri and Ace, or Lauri and a high lottery pick (obviously in hindsight that was aiming way too high). I'm not into it if we are giving up Brown plus a 1st just for Lauri.
I get what you're doing, and I think Lauri would be a decent fit on the Celtics, but his injury history is scary. I'd maybe give up George and one non-Clippers 1st. Not sure the team is any better with Lauri than George, but his age is a factor.