Cousins is about as close to transcendent talent that you can acquire in this league. If you stop and think about it, Demarcus has literally never had any semblance of stability.
Most people agree that a team culture is developed starting with their head coach. However, since he was drafted in 2010, Demarcus enters next year with his 6th head coach. How can any continuity be developed for a team towards a winning culture, when they pull the rug out on their star literally every year. It is kind of amazing he has been as successful as he has.
So yes, if you have an opportunity to trade for demarcus, you take it. He could be the pillar we continue to build and contend around. Lock him up, let him buy into the celtic tradition and mantra, and boom we have that superstar. Plus, even as a 25 year old, his game isn't built around ultra athleticism. This would mean that as he continues develop, or as he ages, he should have a large window of ability.
Get boogie danny. Just do it.