"Apple also has nothing to gain from completely closing off OS X. It would destroy their developer base and be really bad PR" That is the situation today. But

"Apple also has nothing to gain from completely closing off OS X. It would destroy their developer base and be really bad PR" That is the situation today. But a few years down the line, when the vast majority of apps are signed, we find ourselves in a completely different environment. One were it becomes possible to prevent untrusted apps altogether, because there's not that many of them, and it will help "protect" users. They're doing this now, to create an environment where they can do more in future. This may not actually be their plan, but it strikes me to be a very likely outcome. There will be OSX jailbreaks of course. But how many people are going to feel comfortable voiding their warranty on an expensive Macbook?