A language that changes will alienate people, and lose people. Perl saw this. Python is seeing this. The way to guard against this is to keep backwards compatibility. That generally doesn't allow enough change in languages that provide enough constraints to make them popular for large engineering projects, whether open source or commercial. Lisp doesn't need to change much, it's malleable enough in many respects that you can implement whatever you need, but good luck getting large engineering projects done and maintained using it. Perl has the same problem.
The only solution I see to stay relevant is to allow alienating users, but make sure those changes that alienate users are good enough to draw substitutes, enough to keep steady state, or preferably still grow slowly. Maybe prior users will even swing back in occasionally, and without the false sense of betrayal, they'll actually find they like the state of the language a few years later. For a while, at least.
This seems like the end of the world to Python community members, and it seemed like the end of the world to Perl community members because of the prior status those languages held, where they are or were at the top of their respective niches. I doubt the Scala community worries about exactly the same things.
Put another way, did you expect to still be writing Python the same way in 20 years, with only the popular libraries changed? If you did, did you think about what that would mean for the language, and what the community would look like at that time? I'll tell you. Perl. That's not necessarily a bad thing. I write Perl professionally, every day. I love it. It's not the worst thing, being stable and reliable. But you don't get to be top language in your niche and sit on your laurels at the same time.
Change is good. Embrace the change. If you're lucky, you'll use many languages to program in your life and be happy. The only way I see anyone being happy using any single language forever is to bury their head in the sand and ignore everything else going on around them.