Making this move sets up the N.B.A. for something resembling normalcy in 2021-22. The sudden shift to a December start, even if it is accepted by the players, would create chaos across the league. [...] But making sure the 2020-21 season ends in July at the latest would increase the N.B.A.’s readiness for a traditional October-through-June run in 2021-22, which appears to be its next real opportunity to regain access to the crowds, sponsors and ancillary arena income that, as Silver said in May, typically accounts for 40 percent of the league’s annual revenue.