There is a key difference being being able to afford to buy anything, and actually being able to buy anything. The competing founders need to be willing to sell. If a competitor arises that is mission-driven, Facebook cannot buy them.
A direct threat to Facebook is unlikely to succeed. More likely is a competitor based in a niche where Facebook cannot enter for structural reasons that slowly out-competes Facebook on Facebook's turf.
One possible niche is the privacy-focused community. Facebook can't flip all of those users, ever. If something privacy-focused emerges that has low-maintenance utility for the broader world, Facebook's days are numbered.
Can anyone help me brainstorm what features would be compelling for a privacy focused social media/event planning/group discussion platform?
Facebook's network graph is its single most-valuable asset. Responsibly placing it back into the hands of its users will require some subtle care, both to avoid Facebook's ire and to avoid abuse.
Bonus points if you can do it with your spouse and children by your side.
But granted, mission-driven people are less common. To the point that many people who are not fundamentally mission-driven truly do not comprehend that some of us are. We all have our own motivations.
https://dealbook.nytimes.com/2012/04/09/facebook-buys-instag...
At this point in time it will take an act of God to fix it, the lock-in is very strong and their ability to buy up anything that even begins to compete with them serves to cement that lock-in to the point where I don't see a way of ever dislodging it.