There's different ways to think of pace. The pace stat measures how quickly you shoot, but I think what Brad wants is the players to move and think with greater pace, move the ball quicker, cut quicker. I don't think that's a change of philosophy, nor does it require a small ball approach. Just do what we've been trying to do better and more quickly.
These are good points all, and I would add two things that are critical for coaches at this level: 1) getting into the offense quicker; and 2) generating more early offense.
These two overlap in how fast you're getting the ball up into the front court after you gain possession. Boston is middle-of-the-pack when it comes to forcing turnovers, meaning that the Celtics are getting the ball off of made baskets or defensive rebounds a lot, which are both farther back. One simple solution is to advance the ball with a pass.
Among the starters, Brown, Tatum and especially Irving are highly effective in early offense because of their ability to attack the defense off the dribble. For a middling offense that doesn't get a lot of free throws, getting in the paint in the first seven seconds is a logical goal.
I've always remembered Tommy talking about the 1960's Celtics: "We ran on everything. We ran on made free throws."