The signing of Kemba Walker is tremendous for Boston. Not only did they find their point guard for the future, but they found a replacement for Kyrie Irving.
Kyrie and Kemba are similar players with very similar play styles, but I think Kemba can take Kyrie's job and run with it.
The Celtics seem to always be involved in trade rumors when players become available. The Rockets have a few players who could help the Celtics, some way more than others.