If Apple keeps on with all their locked down "security" stuff, it should end up being pretty close to their famous 1984 ad but just reversed on itself.
I think that is a very narrow and skewed view. Every user study has shown that by far the majority of users really like it when their computing platform is not beset with security problems, and that they are willing to make minor concessions to get that sort of piece of mind. Security is still the HUGE advantage iOS has over Android, and that the Mac has over Windows. It's a selling feature, and it's draw is not lost on Apple.
Plug-ins and extensions are, and continue to be, a big security problem for Safari. Even many of the most computer savvy among us has been hit by adware or malware masquerading as a legitimate Safari extension. Folks still download fake Flash updates, "graphics codecs", "search enhancers", and DNS changers. These are a scourge. It makes sense to eliminate the vector that they take advantage of.
It's not like we will be losing any functionality. In the future many add-ons to Safari will be apps instead of extensions.
If you really want an extensible Web browser, Apple isn't preventing you from having one. There are literally over 100 Web browsers available for the Macintosh. Quite a few of them work with either Chrome or Firefox extensions.
I don't see "security" as a bad thing. In fact I see it as quite a good thing...in fact, it's the main reason a lot of people use Macs.