In fact, it's a highly beneficial behavior, and one that is completely optional (and always will be).
[Citation needed]
[...] Or for the fact that it always will be? Um, it's impossible to cite the future.
OK, so you have no evidence. Of course, it would be easy enough for Apple to issue a written guarantee that they won't lock down OS X.
It's just absolutely absurd to think Apple is going to make this mandatory. It would break the Macintosh. What makes you think Apple would be so stupid as to do that?
Why would it break the Macintosh? So long as they offered approved Apple developers a way to unlock the machine for $99 a year and run their own code, who would be impacted?
You are jumping at shadows. You are imaging some Grand Scheme that doesn't exist. Apple has in no way ever implied that they intend to lock down OS X like iOS.
OK... So why doesn't iOS have a similar "unlock" option? They could have made iOS work just like this new OS X feature. Why didn't they?
And to put it the other way, why wouldn't they make OS X like iOS? They've been wildly successful with iOS.