This goes out the window the first time you get real users, though. Hyrum's Law bites people all the time.
"What sorts of things can you build if you don't have long-term sneaky contracts and dependencies" is a really interesting question and has a HUGE pool of answers that used to be not worth the effort. But it's largely a different pool of software than the ones people get paid for today.
Not really. Many users are happy for their software to change if it's a genuine improvement. Some users aren't, but you can always fire them.
Certainly there's a scale beyond which this becomes untenable, but it's far higher than "the first time you get real users".