Was talking to my grandfather yesterday about this very thing. In what world do people live in where they think Netflix, or any service, can continually add new subscribers? At some point it's going to dramatically slow, plateau, or drop.
Everyone knows there's only so many subs you can sell. But the key thing for NF is making sure they can convince everyone they are a tech company and not a stodgy consumer company that is tapped out growing at 3% per year. If the markets ever classify NF as a "boring tech company" like Cisco, Applied Materials etc... the company will drop like a rock if their financials keep sliding.
IMO, a company like NF which is simply a subscription company with a canned product offering across a few tiers is as anti-tech as you can get. It's just that it involves bits and bites so people lump them into the likes of MS, Apple and Google. NF is closer to being a movie making studio + telcom provider selling subs.
I think what hurts NF more than the number of people out there is the fact theres other TV/movie subs competing and only so many people will sub to more than one. It looks like Disney is the service that has really kicked NF in the butt. All the other ones have been around for years and didn't seem to make a dent into NF growth. Disney+ is already at 40+M sub plans after 2.5 years.