No. You didn't read my comment fully. Companies already support app versions that are years old, for various reasons — the most obvious one being that many people use older devices that run an OS that's no longer supported by the app in question, and others just don't ever update anything. So since they're already doing this right now, and have been doing this since forever, there's literally zero additional work involved.
Besides, no one is asking them to "deliver new functionality at a rapid pace", especially to feature-complete products. This whole "keep flapping your wings or you'll die" thing is a lie. It's fine for a product to be done. It's fine to stop. It's fine to go into maintenance mode.
Maybe there should be some sort of condition, like minimum MAU or something. Only regulate those that grow to be huge enough for many people to depend on them. This would exclude startups but would still apply to Facebook and Twitter.
Besides, no one is asking them to "deliver new functionality at a rapid pace", especially to feature-complete products. This whole "keep flapping your wings or you'll die" thing is a lie. It's fine for a product to be done. It's fine to stop. It's fine to go into maintenance mode.