My Problem with Signal

After my morning post about facebook here:

https://steempeak.com/socialmedia/@nealmcspadden/facebook-sells-out-again

I was turned on to Signal: https://signal.org/

It's a messaging app that has no tracking and is end-to-end encrypted.

That sounds great. How much does it cost?

It's free! Awesome!

But here's my problem. Free without ads, tracking, and all the rest is not a sustainable business model.

They are definitely spending money though. The site has a section on developers they are looking to hire. From the job description:

Benefits
You can work anywhere in the United States. Whether it’s your favorite coffee shop or your living room, Signal gives you the flexibility to work wherever you will be most effective. We fly somewhere new once a quarter so that everyone can meet up in person.
Excellent healthcare, vision, and dental with all premiums covered.
Our 401(k) plan matches your contributions (without any vesting period) up to the employee federal maximum of $19,000.
We're stable, well-funded, and capable of focusing on what is best for users without distractions.
Feel good about what you do. We believe in solving real problems, working with integrity, and sharing that work (and code) with everyone.

We're stable and well-funded?

OK, great. But those funders (investors) are going to want to make money someday. Which means either there will be advertising/tracking/whatever or they think they can create a takeover target - at which point the new owner will install advertising/tracking/whatever. There's a third possibility that after the app reaches sufficient mass it will go paid or freemium. This isn't Dropbox or Evernote level of ubiquity though. There are a lot of messaging apps out there.

All in all, it just doesn't look like a sustainable model to me.

Can someone point out where I'm wrong?