ViacomCBS had a compelling presentation Wednesday to illustrate why TV lovers should sign up for its newly branded flagship streaming service, Paramount+. But the most important point company executives referenced — one that will define the success of the service — came fairly late in the nearly 3-and-a-half-hour investor day event. ViacomCBS showed a slide showing the uptick in the average amount of subscription streaming services to which American families subscribe. That number, the company said, has gone from 1-to-2 in 2016 to 2-to-3 in 2019 to 3-to-4 in 2020. ViacomCBS suggested it won’t be long before households subscribe to five or more services.