Marc Stein: The NBA has begun collecting data on available arena dates at G League buildings and practice facilities through the end of August — as well as teams’ regular arenas — as it holds of hope of resuming the 2019-20 season, league sources say. In the strain to find silver linings amid this crisis, there are teams out there eager to see if real NBA games in the summer would be as “hot” as some believe — since there certainly is a pocket of power brokers in the league intrigued by an Opening Night on Christmas calendar.