Wow, this doesn't cover models that have worked for companies like Microsoft or Apple. Were they viral, or did they depend on big LTV? Not completely. LTV helps (people buying iPhone again and again), but they are not subscription-based companies. I think this model falls short to describe business.
MSFT and AAPL both benefit from immense network effects, which translate into high LTVs (Windows/Office platform, iOS ecosystem). The presence of a strong network effect can often be a strong driver of virality, if not a prerequisite for viral acquisition for a lot of businesses because the incentive to share is directly correlated with the value delivered to the user/customer.